I bought all the expansions in a Steam sale (I think it was like $5 or $15 for all of them, couldn't press buy fast enough). You're definitely right about BNW having a lot more to do between turns. I kind of forgot that World Congress was part of the expansion- I can't remember playing Civ 5 without it. It's one of my favorite parts of the game, though I do wish it was a little easier or possible to get other civs to form a voting bloc.