If you guys play with mods MCCommand Center has a setting that rotates which sims show up from lot to lot. It's not 100% perfect (especially if you're going to lots where specific sims tend to show up like the dance clubs or the art centers) but does lend itself for a bit more variety. I haven't played around with it a lot in terms of the retail system so I don't know if it encourages different sims to show up but I did play one store for several days in a recent save and didn't have the exact same sims come in every day like I have in past saves so maybe it does?
This doesn't change the fact that this is something that EA/Maxis should look into tweaking if possible especially if the game is going to be around for a while but it's a work around for now.
