I've never used the fun add-on, but I do have the main mod in my game (or more specifically, the TS8 flavour of the mod), and I've noticed a marked improvement in responsiveness and general autonomy of my sims after installing it in my game. Unfortunately, it appears as though he is testing the fun add-on and it is currently unavailable, but hopefully in a week or two he'll have a new version back up on the site. The main part of the mod should get your sims to respond faster to their own needs or your commands, whereas the optional add-on to the mod 'Fun Is Actually More Important Than You Think' will 'nudge' sims with full needs to go and find something fun to do. In particular Quicker Sim Autonomy & Simulation Lag Improvements - New Addition More Fun Pushes, which aside from improving simulation lag should 'nudge' your sims to do something when they're idle.
You could try coolspear's mods (you'll need to make an account).
