Finally, I did come across research that suggests that while people believe that spoilers are bad, enjoyment is actually increased when you know what is coming (because of cognitive dissonance, or something like that). The reason I didn't include that in the OP is twofold-
1. I think it's disingenuous to tell people who avoid spoilers, "Ha, you don't know what you really like." Not just disingenuous- kind of obnoxious.
2. It didn't seem like the research had a very large sample size or had been replicated. I am leery of these types of social science nuggets that haven't been replicated yet.
That said, it would be interesting if true.