"Yeah, Dave."
I used to write a bit of fanfic myself, among a group of other fanfic writers working with the Pre-Crisis DCU "playground," and not one of them was writing fanfic with the hopes of breaking into comic-writing. It was done for fun and as an end to itself. The only fanficcers I've ever seen who hope to break into comic writing through their fanfic tend to be the very young and very naive. They're certainly the minority in my experience.
As I found that I enjoyed writing the characters I created myself much more, though, and I found that I really HATED writing super-heroes, I finally decided to quit fanfic a few months ago. Now I write exclusively with my own characters except for those in collaborative stories which require at least some writing of other people's characters and their interactions with my own. In the long run, I've found it more satisfying to write. Superheroes don't interest me much except as an occasional novelty. If I ever do write fanfic again, it'll probably be with a character like Swamp Thing, who hasn't been seen in a while in his own magazine, or the original Challengers of the Unknown, or the Blackhawks, et cetera -- all characters who aren't being published any longer and who I miss. It's never occurred to me to write stories based on characters that are still regularly published -- what's the point???