I'm surprised simple endorphins havn't been mentioned, not even by those studies you cited Jeromy.
Without citing anything - I'm going to stick with this, which I used to do with my buddies before we'd go out, ha.
When you eat something super spicy (I'd just eat raw habaneros) and experience intense pain, you get an endorphin rush. Endorphins feel good. That's all.
If you think about it though it's a bit weird, because that's the same reason people purposefully cut themselves (the word for that pathology alludes me at the moment) and other things in that domain - except I'm (and I believe those who crave it - I never got to that level though) doing it by eating a spicy pepper.
"enhancement of the taste of bland foods, postingestional effects, or
I can understand the enhancement of bland foods...yeah that's always good....and the social rewards from looking like a badass. However, spicy peppers don't seem to be too favorable for almost anyone "postingestionally" unless you want to experience pain.
I could see how if people really liked the taste of hot peppers/chilis they'd want to be desensitized to them too. Haha it's funny though that they become immune to ammonia in the eye. That sounds painful.