I'm not sure if it helps performance, but you can use the sims 3 game selector 3.0 which will disable specific expansion packs which makes it like they are not installed.
As for store content, if you copy your downloads folder, your store content should be in there. Open it up and have a look to make sure. If you do a reinstall, once you have a new sims folder, you can paste the downloads back in there, and then reinstall them.