Spore will be modded, the number and quality of the mods would depend on how easy spore can be modded but even if its incredeble hard to mod.... it will be done, there is just no other option.

Sure you can find it desturbing or even wrong for others to make mods, thats your opionon and you may think that. But it will still be done

Though i do not think a random player would end up with a random modded creature and just see his game crashes while doesn't know whats up, modders ain't that dumb (most of them, anyway) nor is maxis so stupid to let that happen, once modded creatures are beginning to come up, maxis would probably make sure you can't download them unless you have the mod too