I'm on the fence about "The Simpsons". There are times when I just want to go "Geez, how much more are we going to get?" (I hear the voice actors have been signed through Season 24), but then there are also occasions where I find myself able to appreciate the modern episodes for what they are, even if I know they'll never be as good as the first eight seasons were.
As for "Family Guy", I hate it, but I don't think it deserves cancellation - I think it deserves an overhaul in its writing staff. The show has loads of untapped potential that it's content to waste on the same agonizingly unfunny antics that we've come to expect from it. Some new blood behind the word processors might be just what the show needs to get back on track.