I agree with Noravea that the most recent seasons were a bit better again (almost coinciding with Marge's new voice in the German version). I am quite fond of the Simpsons (and so are my kids), so I don't see why having more episodes which range from "quite OK to good" hurt the excellent ones.
However, come to think of it, it might be even better to have them a few years in hibernation, followed by a re-launch. The idea how a TV series should be constructed has changed a lot since 1989. That way "The Simpsons" could adjust to that.
I very much enjoy the episodes which flash back to the past or towards the future, and I think that if the Simpsons ended in 1998, I could accept that if...
...they reappear every decade for 2-3 seasons (perhaps 13-episode-seaons only), which would have sort of an event-character having adjusted in age, the characters being allowed to develop (sometimes the writers seem to yearn for that, especially as the things Bart and Lisa experience are in some episodes quite stretched, most extremely when Bart drives to Utah to marry).
Also that would mean that during the breaks, a good deal of satirical potential has built up which writers can tap. The possibility to develop actual story archs might be a benefit, too.
So, for example, seasons 10-12 run in 2004-06, with Homer and Marge in their 40s, Bart struggling with the final years of High School, Lisa in full puberty, Maggie in Elementary School.
Seasons 13-15 run in 2010-12, starting with Homer's 50th birthday, ending with Abe's funeral. Bart is struggling in joblife, Lisa is at college, Maggie a teenager. Mr Burns gets ousted by a hedge fond - for good. Ned Flanders rises as a politician on the tailcoats of the Tea Party.
I can't wait for season 16. All participants already signed up, but they will not start production until 2016, I heard.