Yeah, message boards certainly weren't a magic formula. I've been lucky in that the fandoms I've participated in tended to be large and unusually well-organized. (And the Transformers fandom actually achieved post-modernism, somehow.) So while there were certainly message boards for each that were sewers, a few broke through that managed to sustain above-average internet discussion.

I think you touch on the two factors that I like most about those functional boards- the larger scale of interaction, and the ability for people who don't already know each other to engage in a conversation and create a relationship. Everyone I interact with on Tumblr, I met elsewhere.