It's tricky - and good - because it depends on how you play your game. The Tribal Square [12] provides almost enough people as one house [4]; 5 goods at no cost, which is worth maybe 1 alchemist [6] (which needs a 1/4 of a house to populate) [1] + the gold from a house + around a quarter of a production building [3]. Well, well, it looks like I've talked myself into it, even though it doesn't look like it provides much.
Now to find the space for it. I suppose I could always delete one of my nine military buildings :O