In cube basics are just bad cards. This isn't legacy with Price of Progress and Wastelands, it's a format with very little nonbasic hate so being able to upgrade a basic land to a good nonbasic is much better than upgrading a good cube card into a slightly better cube card. I'd never pass Loothouse to upgrade a Magma Jet or Fire Imp.
My 630 Card Powered Cube
My Article - "Cube Design Philosophy"
My Article - "Mana Short: A study in limited resource management."
My 50th Set (P)review - Discusses my top 20 Cube cards from OTJ!