I have to admit I considered not starting with this section of my discussion because it's only one part of a different point I'm working my way to, and there's been loads of debate about it already. I rather felt like I was just treading on very re-hashed ground by bringing it up. However it would be difficult to discuss the cave demons without going into why they appeared in the first place or what they were supposed to be doing :)

I agree though that by trying to obscure where they were heading with Spike the writers created a lot of room for discussion both about Spike's motives and what he intended to have happen. And like thismaz says above, some of the different possibilities aren't necessarily incompatible!