I don't know yet. I ended up getting the deluxe edition as a gift, so even if I bought this, I'm kind of on the plus side. The price per hour played is very good if I'll play even one game with each new civ. If there's a significant preorder bonus, maybe I'll preorder, but I don't really like exclusive preorder bonuses (especially if they make multiplayer incompatible with people who don't have it). Just waiting for more information.
I can see why some people are so reluctant to buy the expansion, since there are many things about the AI and the UI that bother me as well. Like when starting the game, there's this "continue" button without any other option and nothing significant to see, so what's the point? "No, I don't feel like continuing, I'll just leave the game there forever"?