Well, I say that the Simpsons was hardly the first. After all, Flintstones and Rocky and Bullwinkle were the first "prime Time" cartoon series aimed at older audiences... though they had a huge youngster following (much like the Simpsons does).Honestly I hope they outlive Family Guy, I like the Simpions better. They may not be as good as they once were but I think there is something to be said for being the first .
That said, I hardly think Family Guy will last the 10 year mark. I love FG and all, but it's ran out of steam the last 2 seasons. I think they should focus their efforts more on American Dad, as it is a vastly superior show, and actually has levels to it outside of pop culture jokes. I still think Robot Chicken does what Family guy wants to, and always wanted to. Just act as a random bunch of cut scenes that make fun of pop culture.
But the Simpsons is an American Classic. Even though after the first 11 seasons, it's been on and off. And Lisa should NEVER be the focus of any more episodes for a long time. And Sideshow Mel, Cletus, and Ralph Wiggum should be treated as characters, and not catchphrases. Though, in all honesty, they need to find a way to kill Cletus off. The one thing Family Guy does better than the Simpsons, is that they know how to handle annoying characters that are over used. They killed off the Evil Monkey, The Vaudeville Guys (though they brought them back as ghosts), and Paddy tanninger the Caddy manager. They still need a way to finish off Herbert, though.