Heres what I would do.
1. Cancel all current shows except Spongebob, Fairly Oddparents, Jimmy Nuetron, and Hey Arnold.
2. Give Fairly Oddparents back to Butch Hartman
3. Bring Back old shows Rocko's Modern Life, Angry Beavers, Invader ZIM, Action League NOW!, Kablaam!, and all the game shows
4. End all team themed stuff on Nickelodeon
5. Get rid of all live-action Nick shows EXCEPT Drake & Josh (I actually kinda like this show)
If Nick did this they would be THE greatest channel on TV, but they don't I guess.