*Cough* wonders of the world *cough*.
Oh hell, why not? They're always fun, give a focus for players to compete over. The only thing is there probably shouldn't be too many. I think the wonder inflation (deflation?) of Civ and Galciv expansions dilutes their interest.
The only thing I didn't appreciate in the addition to Wonders in GalCiv2 expansions were the exclusive ones. Having a wonder of the world that only you can build to start with defeats the purpose of having it.
That being said, I believe that was a workaround, to apply civilization-wide bonuses and such.
I'd love mega projects, of which there can only be built one per planet (all mutually exclusive), Wonders of the World, of which there can only be one per game (per wonder), and Super Projects, of which there can only be one per civilization.