Another thing the show could consider would be more serialized content. Think about it..how many story lines have moved beyond the "back to zero" reset formula? I can think of only 4 off the top of my head (add more if you can think of them):
1) Apu has octuplets
2) Maude Flanders dies (and Ned dates others, including Krabaple)
3) Milhouse's parents divorce
4) Barney goes on (and sometimes back off) the wagon
I realize the last thing the writers want is for Lisa and Bart to progress into their teens, but there has to be more 'progression' if fans don't eventually get a serious case of the 'Meh's'.