I began to think of some other old stuff that the show could probably do a good job parodying...
1) Greek tragedies or comedies... I think Aristophanes' the clouds or lysistria would be hilarious... especially the clouds... Bart going to see professor frink or the CBG to get educated only to come back frail... and we could have lightning hitting homer (people love to see the guy hit by lightning)
Lysistria (probably not spelled correctly) could be Springfield against Shelbyville likened to the war in the book. We could have an in joke about cousins not sleeping with each other (even though they are so darned attractive to the shelbyvilleians... There are some good possibilities there...
2) Sophacles. I know these are kinda depressing, but they could be great with the simpsons touch. I mean, the riddle of the sphinx, bart raised by wolves, the chorus (I see a musical number there)
3) Beowulf.- could be cool senseless violence? duff flavored grog? moes tavern as herot? come on, there are some cool ideas there.