Althought Civ V does have an inheirent simplicity to it (at least compared to Civ IV, which is one of the biggest criticisms), it has amazing potential should they actually build on it.
First, they need to double or triple the hex resolution. The current hexes are just too large to handle advanced unit strategy and by keeping the land mass the same size and making the hexes smaller, it will also allow a more diverse tile arrangement. This alone would make the expansion worth it, but it's not likely to happen.
Second, we need more tile choices. The larger the tile the smaller the options, since you have to generalize their usage, but if we could have smaller tiles things like air bases, army bases, nuclear facilities supply centers etc could be built. Getting them out of the cities would provide a more diverse tactical environment. Even with the larger tiles, I think there is much lost potential that they haven't addressed ever with any Civ game.
I guess in all what I'm saying is that they should impliment some of the routine civic/military features that virtually every major wargame developer puts into their stuff. No one wants Civ to be another EU or HOI since those are combat driven games, but if they could create some sort of "bridge" it could be amazing.
I'm buying the expansion no matter what since I'm a big Civ V (and IV) fan and I've put in almost 150 hours so far and I have no problem putting in more.