That's the challenge of organizing. Too vague versus too specific. Finding the balance.
Now I hope you all don't take this the wrong way, but I am honestly curious what connection a fan feels exists between Buffy and Firefly that would require both be under one category. Look at it from the opposite view. Putting Buffy in a category like Horror, or maybe better, Supernature, means you would see Cabin In The Woods alongside Buffy, alongside Supernatural, etc. Likewise, you'd go to a Sci-Fi forum for Firefly, Dr Who, Farscape, Bladerunner.
When a franchise becomes too big for a category that it overtakes it (Star Wars, for the example with the most staying power), it should have its own forum. Lord of the Rings and Indiana Jones were once upon a time that big but now they aren't. When that becomes the case, tidying up may very well require they go back from whence they came.
It really seems a lot of the yes votes to keep Buffy come from a sentimental place, one which I feel, too. But rationally, it is currently a small, small franchise.
Still, I didn't vote, because I haven't made my mind up. It's nice to be able to go to one place where there aren't trollish posts in every thread and the members seem to genuinely want to help each other and have intelligent discussions. But shouldn't that be the case of all forums? If not, there are more serious problems going on that probably should be looked at first.