Pardon me if I'm wrong here but having played one game with the expansion, I haven't really found any specific reason why you should focus your empire in building faith and trying to create the best religion possible. Sure, the beliefs are somewhat useful, you can get bonus diplomatic points from another civs who have adopted your religion and you get some benefits with the city states if they share your religion, at least if you're the founder.
However, these all seem pretty minor effects to me. There isn't a way to win a religious victory, which is a huge minus to me. It also seems rather meaningless if some city from another nation adapts your religion as their main religion. You can't see what they're doing like in Civ 4. You can't annex them or puppet them as if they were in awe of your religious superiority (at least as far as I know). It simply seems to make no difference whether your religion is strong or not. Has anybody else thought about this?
Now don't get me wrong. I actually like the religions and I like spreading mine even if it makes little difference. It adds more immersion to the game as I can imagine religious wars, which don't otherwise really exist as a mechanic. However, I do feel that the developers could have done something more with this system.
Ps. Sorry if the thread already existed. I tried to search and only found Civ4 threads.