This weekend I figured out the source of my lagging that I have been having in my game since about the time Pets came out. Figured it might help some others.
It didn't effect every game, but eventually I would start having little lags over and over, and then one big HUGE lag at 4 am every game morning. I figured it had something to do with NPC routing as a lot of bars close at that time in-game. So most of my recent towns had their bars removed just to cure this. It would seem to help in new games, then the lag would eventually come back. I would quit the game, clear caches, etc. and that would help for a little while, but then the lags would come back again eventually.
So this weekend, my game was working good, no lags yet this session, and I sent my sim off on a hunt for gems around town. Fired up the "Collection Helper" thing, and after finding about his third or fourth gem noticed the lagging coming back. This happened to be in the early morning hours and sure enough at 4 am, the HUGE lag came back. After I was done finding gems and minerals I decided to give something a shot and turned the "Collection Helper" back to "none". The lags completely disappeared without leaving my game. And at 4 am the next morning no lag at all.
So I am guessing the game re-spawns a lot of the collectibles at 4 am and if the Collection Helper has one of the categories turned on, the game takes a bit to process the potential of showing you where they are.
Hope this helps anyone else out there having similar issues.