I would strongly suggest Aether Vial. In my experience, you have to be able to cast a mana-based counterspell (Spell Pierce/Flusterstorm/Red Blast), a free counterspell (Force of Will/Misdirection/Daze), and the cheat instant all in the same turn to untap with a Drednought reliably on turn 3. Even then, you just straight up crumble against Abrupt Decay. I'd also recommend keeping Torpor Orbs minimal and omitting Illusionary Mask entirely because they don't do anything else in most matchups now that Snapcaster is out of most decklists. They hose Nic Fit, Elves, and to a lesser extent Taxes well, though. They're worth having 2-3 main, 1-2 sideboard. I have played a Grixis list that looked like this:
So basically, cutting Daze and shaving numbers so you can Thoughtseize a path and use Cavern of Souls. Bob was really good for obvious reasons. The list I posted just here was just for testing purposes and I never played it in a tournament. I imagine Dig Through Time would be good in an updated build, but you have to weigh it against Bob. If everything else went poorly, True-Name Nemesis could usually clog the board against a non-Tarmogoyf/Knight of the Reliquary deck and give you time to piece together a way to cheat a second Dreadnought out. As usual, this deck is bad against Swords to Plowshares and Abrupt Decay. You just have to fade a lot of cards when playing it, which is why I stopped pursuing it.
Well, it's the best card in the Dredge mirror. The trouble with a card like this is that alone, it isn't very good. Non-graveyard based decks essentially run Snapcaster, Dig, or Cruise. Main deck Rest in Peace is a thing now for those reasons and Tarmogoyf/Deathrite and Lavamancer/Life From the Loam nerfing. Leyline is in many situations worse.
So let's do a cost/benefit analysis of Leyline: Benefits
-When used in combination with certain other cards, it is very strong. See above suggestion of Helm of Obedience as well as Pox/Liliana. Hymn to Tourach also becomes much better when delve and Snapcaster possibilities are eliminated.
-If you expect a lot of budget players who will be playing Dredge or graveyard-based combo decks, then it's a good metagame call.
-If you expect a lot of Lands players, it's a good metagame call to have them in your sideboard.
-It can't be destroyed by Abrupt Decay, and spells that could destroy it are found more in sideboards than main decks.
Costs
-You have to play other cards that pair with it to make it good.
-Your opponent's deck has to rely on the graveyard somehow for it to be good.
-Doesn't fully stop Tarmogoyf or Deathrite Shaman.
-The turn 0 benefit is really not a benefit except against ultra-aggressive graveyard decks like Reanimator or Dredge, which seek to use the graveyard as a resource starting turn one.
-Assuming you do not have turn 0 Leyline, Treasure Cruise decks will still get some fetches, counters, and cantrips into the graveyard before you can spend probably your whole turn casting a Leyline, at which point in the game, a 4-mana spell that doesn't immediately change the game is too late.
-Relic of Progenitus, Nihil Spellbomb, and Rest In Peace are in many situations (and, I would estimate, the plurality of situations) better because they immediately clear out everything and the former two replace themselves.
-The first Leyline is the only one that matters, having a totally redundant effect thanks to - like you said - Treasure Cruise decks having no removal for it except counterspells.
-Consequently, the second through fourth Leyline are terrible pretty much all the time. It would take a Maelstrom Pulse, Oblivion Ring, Vindicate, or Pernicious Deed (to name cards that you would could really expect to see maindeck in a tournament) to clear one off the board. So really, assuming you start the game with a Leyline, you now have 3/53 cards (5.67%) of your deck that does nothing to affect the game.
-A double-Leyline opening hand is usually the same as a mulligan.
So my opinion is obvious, but I'm glad we're discussing it, since it is a thing worth thinking about. I know I personally got my playset of Rest In Peaces after I did this initial consideration. Thanks for starting the thread!
Specifically discussing Legacy, I personally prefer no proxies in tournaments. I understand that hampers peoples' ability to participate, but Magic isn't a cheap game to play at a competitive level, just like poker or hardcore computer gaming. It requires a significant investment of money and time, and I like to see that respected by tournament operators. Again, to clarify, I'm only talking about Legacy. I think occasional 9 or 10-proxy Vintage tournaments are fine because otherwise the decks cost as much as a car and 2/3 decks are Bant-driven haterade or Dredge, which, as MTGO and major Vintage events show us, are not an accurate reflection of the metagame. I think players should be rewarded for their financial investment with a degree of exclusivity in tournament situations. I think an LGS doing one or two 10-proxy tournaments a year is fine in both Eternal formats because it helps expand the player base, but any more than that is just cutting into the investment reward. In casual play or playtesting, I would take the opposite view and strongly encourage people to proxy as much as they want so that they can practice with decks in person to get a feel for them. I think getting a good handle on a Legacy deck is really a necessary part of making the investment in one. When I play casually, it's definitively casual. The object of the game is fun and trying out ideas. I'm not going to force my fellow Magic player on casual day to go out and buy 4 copies of Natural Order or Eurekas or something. To that end, the only casual formats I regularly play are Cube and EDH. I don't play casual Legacy because I don't have any casual Legacy decks. So that's my particular take on it.
TL;DR - Casual & playtesting: Yes. Tournaments: Once or twice a year to drum up interest and no more.
Misdirection is a much better choice. 2-for-1 with the reasonable chance of 2-for-2 is quite acceptable. However, nothing is a true replacement for Force of Will. That's why it's expensive. It is the best card at what it does. Mental Misstep is the best at what it does, but it is a recent enough card that Wizards can ban it without a ton of complaints (and, in fact, cheers). My personal use of Foil is restricted to three-card deck format experimentation where it partners with Nether Spirit and an Island. I think Foil is just worse than Counterspell. I'd rather have to hold up two mana to counter things than discard (optimally) two lands to cast a card.
First, I'd just steer you away from LED-less Dredge. Trust me, I've put in the hours. In a deck where the whole point is to win game 1 before your opponent can do anything, sacrificing a potential LED-Faithless Looting/Cephalid Coliseum draw just kills you. I'd also steer you away from Solidarity because I don't think it works without Candelabras. If you have them, good on you, go for it. Otherwise, save that one for playtesting where you can use proxies. I can tell from your post that you are either a Johnny by nature or a Johnny by budget or some combination of the two, and I've long occupied those two spots. I also try to seek out divergent decks, so just know that this is a safe place and I'm saying all these things from a positive head space.
There are a few approaches to this question - and maybe more that I'm not thinking of - but here are my thoughts on these angles:
Financially, Karakas is an investment. Like low-risk stocks or gold or property overlooking an Italian lake, that investment will pretty much go up in value for the rest of the foreseeable future. Huge downward price spikes don't happen in Legacy (for the most part, sticklers) because the format is incredibly stable. Taxes evolves maybe once or twice a year. The following will be a baseline truth of the deck for the rest of its existence, however: Karakas exploits Mangara (though he's clearly out of most lists now) and protects Thalia and Brimaz for free. These are two cards that probably aren't going anywhere for the foreseeable future. Taxes passes in and out of highest-level status, but it is consistently a good (albeit meta-dependent) deck. Karakas is a good investment because as long as Brimaz and Thalia are viable in Legacy, people will play 3-4 copies of Karakas. Legacy changes over the course of months, usually, so if there is a price slide thanks to, say, a huge uptick in Wastelands or a newly spoiled Super Phyrexian Revoker Xtreme Edition that everyone jams into their decks as though they were Treasure Cruises, you'll be able to see the slide coming and hitting. You'll have a matter of months to sell them off; you'll never wake up on Black Tuesday and find out your Karakases aren't worth anything. So in this sense, Karakas is just a good financial move.
Playability would dictate that you should grab as many Karakases as you can. It is by far the most unfair thing you can do in a deck that is almost entirely fair. (Second would be Mom.) It's a deck full of cards that make everyone play fair. Containment Priest, the latest addition to Taxes sideboards, is the ultimate illustration of this. It was printed specifically to blunt reanimation, Natural Order, Oath of Druids, Aether Vial (which is, ironically, only played in Taxes {sorry, Merfolk and Goblins, you're not really decks as much anymore}), and, most notably, Show and Tell. It even plays nice with Batterskull so you reeeeally get the idea. Anyway, many Karakases -> Winningness.
Pride of ownership is quite subjective. I personally don't feel much when people see my cards. I'm not rubbing my Moat in peoples' faces during EDH games like, "YEAH, I'VE HAD THIS SINCE '94!" I also don't care much about whether my car is shiny. However, like guitars (of which I own a number), there are stories regarding certain cards - in particular the physical wear on them - that I think are just good stories of the Wild West days or have personal significance to me. I traded a Plateau to a predatory older player for a Baron Sengir in 1995, and I now keep it in my trade binder. Whenever a fellow fogey points it out and gives me props, I tell them about that trade. Same with my Arabian Nights Mountain, which is the first Magic card I ever saw. Currently, a pristine Baron will set you back about 5 bucks, which is 70 less than an Unlimited Plateau. And you know something? Nowadays, with my current income alleviating but not eliminating the financial barriers to playing the game, I'd do it again. I got supreme Timmy joy from that Baron Sengir compared to that Plateau, which featured a color I never played (red). It would have probably been used in a deck with white as a means of throwing off my opponent and providing a better Strip Mine target than a Plains. The Chrysler LeBaron is very beat up from many sleeveless years of being windmill slammed onto concrete at my school. I kept it even when I sold most of my collection in the early 2000s just before the Type 1.5 price spikes started happening. Bad market read on my part, but I was frightened by the horrible management of the Pokemon Trading Card game's secondary market values. Anyway, my point is that you'll presumably retain those Karakases for many years to come. I think that has at least some value, but like I said, it's totally subjective and you may not care about Karakas any more than you care about Tolaria.
4 Misdirection
1 Gitaxian Probe
4 Brainstorm
2 Vision Charm
4 Stifle
3 Reality Ripple
4 Thoughtseize
2 Hymn to Tourach
2 Torpor Orb
3 Aether Vial
2 True-Name Nemesis
4 Phyrexian Dreadnought
4 Dark Confidant
4 Polluted Delta
4 Scalding Tarn
2 Underground Sea
2 Volcanic Island
1 Swamp
4 Cavern of Souls
So basically, cutting Daze and shaving numbers so you can Thoughtseize a path and use Cavern of Souls. Bob was really good for obvious reasons. The list I posted just here was just for testing purposes and I never played it in a tournament. I imagine Dig Through Time would be good in an updated build, but you have to weigh it against Bob. If everything else went poorly, True-Name Nemesis could usually clog the board against a non-Tarmogoyf/Knight of the Reliquary deck and give you time to piece together a way to cheat a second Dreadnought out. As usual, this deck is bad against Swords to Plowshares and Abrupt Decay. You just have to fade a lot of cards when playing it, which is why I stopped pursuing it.
EDIT: Wrong number of Gitaxian Probes.
So let's do a cost/benefit analysis of Leyline:
Benefits
-When used in combination with certain other cards, it is very strong. See above suggestion of Helm of Obedience as well as Pox/Liliana. Hymn to Tourach also becomes much better when delve and Snapcaster possibilities are eliminated.
-If you expect a lot of budget players who will be playing Dredge or graveyard-based combo decks, then it's a good metagame call.
-If you expect a lot of Lands players, it's a good metagame call to have them in your sideboard.
-It can't be destroyed by Abrupt Decay, and spells that could destroy it are found more in sideboards than main decks.
Costs
-You have to play other cards that pair with it to make it good.
-Your opponent's deck has to rely on the graveyard somehow for it to be good.
-Doesn't fully stop Tarmogoyf or Deathrite Shaman.
-The turn 0 benefit is really not a benefit except against ultra-aggressive graveyard decks like Reanimator or Dredge, which seek to use the graveyard as a resource starting turn one.
-Assuming you do not have turn 0 Leyline, Treasure Cruise decks will still get some fetches, counters, and cantrips into the graveyard before you can spend probably your whole turn casting a Leyline, at which point in the game, a 4-mana spell that doesn't immediately change the game is too late.
-Relic of Progenitus, Nihil Spellbomb, and Rest In Peace are in many situations (and, I would estimate, the plurality of situations) better because they immediately clear out everything and the former two replace themselves.
-The first Leyline is the only one that matters, having a totally redundant effect thanks to - like you said - Treasure Cruise decks having no removal for it except counterspells.
-Consequently, the second through fourth Leyline are terrible pretty much all the time. It would take a Maelstrom Pulse, Oblivion Ring, Vindicate, or Pernicious Deed (to name cards that you would could really expect to see maindeck in a tournament) to clear one off the board. So really, assuming you start the game with a Leyline, you now have 3/53 cards (5.67%) of your deck that does nothing to affect the game.
-A double-Leyline opening hand is usually the same as a mulligan.
So my opinion is obvious, but I'm glad we're discussing it, since it is a thing worth thinking about. I know I personally got my playset of Rest In Peaces after I did this initial consideration. Thanks for starting the thread!
TL;DR - Casual & playtesting: Yes. Tournaments: Once or twice a year to drum up interest and no more.
There are a few approaches to this question - and maybe more that I'm not thinking of - but here are my thoughts on these angles:
Financially, Karakas is an investment. Like low-risk stocks or gold or property overlooking an Italian lake, that investment will pretty much go up in value for the rest of the foreseeable future. Huge downward price spikes don't happen in Legacy (for the most part, sticklers) because the format is incredibly stable. Taxes evolves maybe once or twice a year. The following will be a baseline truth of the deck for the rest of its existence, however: Karakas exploits Mangara (though he's clearly out of most lists now) and protects Thalia and Brimaz for free. These are two cards that probably aren't going anywhere for the foreseeable future. Taxes passes in and out of highest-level status, but it is consistently a good (albeit meta-dependent) deck. Karakas is a good investment because as long as Brimaz and Thalia are viable in Legacy, people will play 3-4 copies of Karakas. Legacy changes over the course of months, usually, so if there is a price slide thanks to, say, a huge uptick in Wastelands or a newly spoiled Super Phyrexian Revoker Xtreme Edition that everyone jams into their decks as though they were Treasure Cruises, you'll be able to see the slide coming and hitting. You'll have a matter of months to sell them off; you'll never wake up on Black Tuesday and find out your Karakases aren't worth anything. So in this sense, Karakas is just a good financial move.
Playability would dictate that you should grab as many Karakases as you can. It is by far the most unfair thing you can do in a deck that is almost entirely fair. (Second would be Mom.) It's a deck full of cards that make everyone play fair. Containment Priest, the latest addition to Taxes sideboards, is the ultimate illustration of this. It was printed specifically to blunt reanimation, Natural Order, Oath of Druids, Aether Vial (which is, ironically, only played in Taxes {sorry, Merfolk and Goblins, you're not really decks as much anymore}), and, most notably, Show and Tell. It even plays nice with Batterskull so you reeeeally get the idea. Anyway, many Karakases -> Winningness.
Pride of ownership is quite subjective. I personally don't feel much when people see my cards. I'm not rubbing my Moat in peoples' faces during EDH games like, "YEAH, I'VE HAD THIS SINCE '94!" I also don't care much about whether my car is shiny. However, like guitars (of which I own a number), there are stories regarding certain cards - in particular the physical wear on them - that I think are just good stories of the Wild West days or have personal significance to me. I traded a Plateau to a predatory older player for a Baron Sengir in 1995, and I now keep it in my trade binder. Whenever a fellow fogey points it out and gives me props, I tell them about that trade. Same with my Arabian Nights Mountain, which is the first Magic card I ever saw. Currently, a pristine Baron will set you back about 5 bucks, which is 70 less than an Unlimited Plateau. And you know something? Nowadays, with my current income alleviating but not eliminating the financial barriers to playing the game, I'd do it again. I got supreme Timmy joy from that Baron Sengir compared to that Plateau, which featured a color I never played (red). It would have probably been used in a deck with white as a means of throwing off my opponent and providing a better Strip Mine target than a Plains. The Chrysler LeBaron is very beat up from many sleeveless years of being windmill slammed onto concrete at my school. I kept it even when I sold most of my collection in the early 2000s just before the Type 1.5 price spikes started happening. Bad market read on my part, but I was frightened by the horrible management of the Pokemon Trading Card game's secondary market values. Anyway, my point is that you'll presumably retain those Karakases for many years to come. I think that has at least some value, but like I said, it's totally subjective and you may not care about Karakas any more than you care about Tolaria.
Hope my long answer helps you figure it out.