Hmm...this is tough. And I say that because, like a few others here have said, seasons 1-3 (and the movie) are classics, while the seasons afterward started going downhill and haven't yet come back up. And those first initial seasons were classics because of the awesome crew they had back then, and a good chunk of them left to work on other projects. In one way, it would have been more of a bang to end the series after such a dynamite movie, but in another way, it is one of Nick's most popular series and I can see why they wouldn't want to let it go. Lately I've been watching some early episodes and some later episodes, and I find it sad that the early episodes get a laugh out of me every couple seconds, while the later ones get a range of 0-2 laughs out of me. I'm not slamming the current crew because I understand how hard they work, but I can see why you guys are worried about the future of the series. ^^;
I do agree that it would be super cool to get some of the old crew back, but I know that more than likely won't happen. But I do think it would be a great idea for Nick to juggle some writers around, maybe get some fresh ideas. I would hate to see such a spectacular series fizzle out.