Cars should be able to breakdown so they have to be towed/repaired. Would give another nice aspect to handy sims. Also being able to give them nice upgrades, so a cheaper car can be made to run faster.
There should also be a mechanic added that makes male sims' facial hair grow. And maybe hair in general. Thatway, you could make more use of the sallon. And add a new interaction to the mirror to shave. heh, it could be another life skill to teach a teen sim. I mean, Sims2 Castaway has your sims grow beards over time.
And maybe bring back the aspect of your sims being able to /buy/ more clothes for their wardrobe. I know it has been mentioned before, but its not as fun to have all the clothes available from the start, not counting uniforms from work.