Two characters come into mind: Wally West from DC and Cannonball from Marvel.

Wally West was very succesful as a character, thanks to good writing right up till he got kids. But before that, he was a sidekick to the Flash (Barry Allen). And then formed a group called the Teen Titans. With Barry Allen's sacrifice in the Crisis on Infinite Earths, he took the role of the scarlet speedster at his lowest point. His speed was not as fast as before and he had to "carbo- load" to re-fuel. And then he discovered the Speed Force. He also had a family of speedsters, which made his characterization more fun to read, as he interacts with each "family" member. He became a member of the Justice League (doubting it was just by legacy and not by merit). Great characterization on that part. Somewhere, the powers may be decided to bring back Barry Allen. Just because they can. Where is he now in the new 52? we have to wait it out, I guess.

Cannonball is not a legacy character, but just like Wally West, he was a part of a teen group called New Mutants (I know the X-men were disguised as superheroes with their masks and all, how do you explain New Mutants? With the name and the X-logo, didn't that give away the illusion they were trying to bring? Perhaps Professor X has created a psychic illusion for the New Mutants, ah well...) He with his southern upbringing is like how Clark Kent could have been if Smallville was like Kansas. His powers give him strength and invulnerability as long as he is in flight and in rapid motion. And he graduates from being part of the new Mutants, to being a heavy hitter in the X-Men. Recently, he's back with his old gang , the New Mutants. Is that a step up, or a sideways walk towards characterization development?

Somehow, art imitates life, as our graduates, go from promising careers to being shot back down to either being background characters... or simply forgotten