When a household has too much money, great toys constantly around them, and LTRs, every room is always well decorated, every seat or bed is such a powerful provider of comfort, etc., for things to even be challenging anymore, it might be time to break off and play grown up kids who are ready to move out on their own. Or maybe start spending some of that money to improve the lives of other sims in town.
For those who might be interested in an extra challenge in this regard: http://www.modthesims.info/download.php?t=432449
I've been using the "Hot" version, the one in the middle of the three, for a couple of years now. It really changes gameplay tremendously, at least it did for me. Suddenly all of the little +5 and +10 moodlets become very important and it can be really difficult even in the best of environments to be able to send a sim off to work/school with enough persistent positive moodlets to keep them happy throughout their day.
Fortunately inactive sims are not affected, only the actively being played household at the time. I would hate to have to keep doing that many creative things to keep the inactive sims around mine happy as well. There's only so much shoving of perfect meals and herbs into my guests, forcing them to sit on overly comfortable sofas in lavishly furnished living rooms playing games to keep their fun levels up, and so on that I can tolerate before I just don't want to have guests over anymore. :)