If I cast Expropriate, and my opponent votes Money, could I take an untapped land & have to come to me untapped (i.e. my opponent doesn’t/can’t tap it before I get it)?
Yes. Since the effect of the spell doesn't ask any player for a mana payment, the controller of the land doesn't get to activate mana abilities during its resolution. And without something asking for a mana payment, you can only activate mana abilities any time you have priority. Which no player has during the resolution of a spell or ability.
605.3 Activating an activated mana ability follows the rules for activating any other activated ability (see rule 602.2), with the following exceptions:
605.3a A player may activate an activated mana ability whenever they have priority, whenever they are casting a spell or activating an ability that requires a mana payment, or whenever a rule or effect asks for a mana payment, even if it’s in the middle of casting or resolving a spell or activating or resolving an ability.
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Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)