yea, they pretty much do only that. Someone even posted a petition asking for a world editor, mainly because they wanted bigger planets.
I don't even know if doing that is even possible, but come on, there are over a BILLION planets! and look at the terraforming tools that we discovered, it would take a lifetime to exhaust all the possibilities. Besides, we don't yet know the full potential of what we can do in spore.
I did post on there to ask maxis about the issue with parts not moving when the lower jaw moves, no reponse from them yet, but give them time.