That's a good decision, Hunter. I also love my Sims 2 and can't imagine to uninstall them.
The Sims 3 look fantastic to me and i'm sure that i will buy them, but this will not make me forget about the Sims 2.
It's like you've said, all the work, the models and creations... where will it go? I wish there would be some kind of transforming tool that can change Sims 2 stuff into Sims 3 stuff. But i think this is very unrealistic.
I also think that all those many machinima artists will stuck on the Sims 2 for a while. It's because you can mod each and everything in the Sims 2 but nobody knows how modding and creating can be done in the Sims 3.
And i can't see too many improvements in the Sims 3. I mean it's great, bigger, better, but not such a huge quantum leap like it was from Sims 1 to Sims 2 in those forgotten days.