Yeah the walls are a little dicey. I just remember going Overgrown Battlement, Overgrown Battlement, Overgrown Battlement => Ulamog in Standard a few years ago, which was always a little sketchy, but fun when it came together. Probably not a thing I should try to recreate in cube, though.
Utopia Sprawl is the #1 most confusing card in my cube for our newer players, moreso than all the weird suspend and dredge cards. "No, you have to put it on a Forest, that's not a Forest. Put it on this Stomping Ground. No, it doesn't make all colours, you had to pick a colour when you cast it three turns ago. Fiiiiine just pick blue now even though I'm pretty sure you used it for black already."
Good post Eric. A+.