I hear you on the little fandoms stuff. Not only are there usually less canon stuffs to worry about, there's less of a chance that the fangirls will have invaded. Plus you get to explore where others have not yet done so. Woot.

My reason for not writing Buffy or BSG is because it's too dense. There's sooooo much to remember, and the character interactions are so multilayered, I couldn't do better than the writers. Plus, Joss-verse stuff has its own speech rhythms and I could never do it half so well as he does.