I really think, that Spiderman needs a Reboot too, but the owners of the franchise doesn't.
At first about the confirmed casting: Tobey Maguire and director Sam Raimi both will be returning. That seems to be sure. And Kirsten Dunst? Maybe..

And Mary Jane Watson will be coming back as well. If Kirsten Dunst decided to reprise her role, Sony would be glad to have her. "Sony would never recast her."

Rumors about Spider-Man 4: Don't expect the fourth film to be dark like "The Dark Knight" or even "Spider-Man 3." "The difference between Spider-Man and Batman is that Batman is duelling with a dark side of himself, and that's not what Peter Parker's struggle is. Peter Parker has no dark side himself. In Spider-Man 3 it was the black costume. Peter Parker's struggle is about sacrifice."

And now about the possible Villians: " That should lead to speculation that Dylan Baker's character of Dr. Curt Connors will ultimately turn into The Lizard as he did in the comic books. There's one other character that's been set up but is a real longshot -- Daniel Gillies, who plays John Jameson, the astronaut fiance of Mary Jane in "Spider-Man 2." In the comics he becomes the villain Man-Wolf. Raimi has said in the past that he wants the best actors to play the villains in the movie, not necessarily the most famous.
Source: www.worstpreviews.com