There's a great discussion on this topic going on over at Karen Miller's blog.
Here is part of what I wrote in the comments section:
I must admit I have never read fanfic and have no desire to do so. Nor do I have a desire to write it. In fact, I don't "get" it. One of the great joys in writing for me has always been world building. To use someone else's world - or even worse their characters - would take away 90% of the joy!
Sure, I wanted to be published, but that was never the obsession. And if I'd reached the end of my life unpublished, I would never have thought my life wasted. I wrote because I had to - that was the obsession - writing was and is an inseparable part of life. It has been since I was eight years old, or even younger. Does someone who reads a book, or goes sailing every weekend, or horse-riding, or swimming at the beach, or to the opera, waste their life? Of course not!
And that perhaps is the best advice I can give to a "wannabe" who is not sure whether they have what it takes to be a "got-there"! If you aren't loving the journey, if you ARE going to give up on the creative process after constant rejection, then you are probably in the wrong business and, yes, wasting your life. If the creation is what counts, then publication is just the icing on a cake that is already tasty. If creation is what counts and brings you joy, then you have a fufilled life no matter what happens.
Don't fall into the trap of thinking that publication is what writing is ALL about. It's not.