My game plays just fine but a few days in, I wanted to play Sims 2 so I uninstalled Sims 3. I saved all my files onto my desktop so when I reinstalled Sims 3, I would still have my games.
I got as far as "I uninstalled Sims 3". Why not just keep both?
I like to switch back and forth, depending on the playstyle I want. Unless you have severe hard drive space issues, you might just consider having both installed. Uninstalling and reinstalling sounds like a hopeless waste of time.