I honestly think that Matt Groening and David X. Cohen are taking an intelligent approach at resurrecting Futurama. I honestly think that Futurama hasn't dramatically changed with the DTV Movies. In fact, if memory serves, Bender's Big Score, The Beast with a Billion Backs, Bender's Game and Into the Wild Green Yonder are supposedly Futurama's fifth season combined with all four movie releases to be later cut up into individual episodes, with a little added content to make the episodic mini-series have better flow to the fifth season. However, I may be wrong here.
Regarding Invader Zim: It has already been established that there are no plans to revive this show, despite it's fanbase, that and we already know Vasquez's sentiments about working with Nickelodeon again, and frankly, I cannot say that I blame him for hating Invader Zim and Nickelodeon.
Regarding Hey Arnold! -- I honestly was hoping to see the Spinoff that was centered around Helga Pataki and her dysfunctional family, but that's not going to happen anytime soon.
However I will agree that if there is a large potential fanbase that's willing to make mountains move to get their favourite show back on the air, it will happen. The fans just have to be there, otherwise, it's just another online petition with five signatures wanting something that's never going to happen, unless you're into fanmade concepts that're nowhere near as good as the original show was for its time.