Terrain paints will cause unstability, which I notice you have quite a few of. Also, objects should not cause instabilty, they should just get replaced with Maxis defaults.
Going through your Downloads folder with the Clean Installer, I noticed quite a lot of empty packages and duplicate files.
My bad. I'm a little nervous about deleting duplicate files. I did that once and some meshes stopped working but I'm willing to chalk that up to being a noob and figure I must have done something wrong. I was going to leave the terrain paints as the file sizes are small. The only ones I knowingly imported were for the beach - I really wanted the sims to swim in the ocean. The other ones I must have missed when I was installing some lots.