Technology wise, it's easily done and possible. Other reasons though, I suppose how much you tweak and use it as a base. If you just do one or two things or whatever, use the same textures, etc, then there may be some minor troubles involved. If you really change things up, use your own textures, etc, then it should be fine as you'd be doing little more than 'sketching' it out in Spore.
At any rate, you'd probably at least have to really clean up the models. They don't always come out clean. Plus, since Elemental is played much more often far away, you could likely take out a bunch of polys to help optimize it.
