darth_ender said:

Now if The Simpsons were more like a soap opera, introducing new characters, introducing new plot threads and twists, tying up old ones in haste, and all the characters aging and moving on to more lucrative careers, then I would love the show again. That sounds like a recipe for hilarity!

I don't know about all that, but the Simpsons have had quite a few changes in the status quo over the years.

People died, characters dealt with death, relationships changed, people got divorced. Characters have changed and come back (Homer's brother, sideshow Bob, Marge's prom date)

For the one show on TV that has no need to ever change, I think that's a fair ammount of progress.