I actually read quite a bit of Star Trek fanfic too -- though this was the licensed stuff. I went through a phase where I bought (usually at secondhand stores) a ton of books written about the Next Generation characters -- I still have one of them, and I really like it.
What appeals to me about fanfiction is the fact that the world building and characters are already set -- I think it gives the writers freedom to explore other things, since they know their readers will already know the foundation. These days, I mostly read Harry Potter fanfiction, and since I've been reading it for a while now, I have a list of authors that I know will write good stories -- and as a reader, I love the relationship aspects which are explored in more depth. That's also what benefits me the most as a writer. Even though it's more challenging to delve into some of the more complex relationships when you're also setting up the world and establishing the characters, it gives me a goal and ideas of what words (for me, as a reader).
I've also been reading an online serial -- probably not something which would appeal to everyone, but for me, it's been very helpful, as the MC struggles with internal perfectionism in a very similar manner that D does. Even though he's an adult, I've learned so many things about perfectionism and possible ways for me to handle it.
All this helps explain why my book reading has dropped this year. I'd hoped to increase the number of books read, but as we near the half-year mark, I'm quite a bit behind my total for last year. *sigh* But it's not because I've stopped reading -- I'm simply splitting my reading time between books, online reading, and some fanfic, as well. Overall, I'm probably reading more (in amounts of words read) than ever before...but I'll keep working on that balance :)