Todd, that's really awesome. I had a feeling if anybody was going to do this, it might have been you.
Kudos.
I would say definitely allow for the anecdotal, trivial stuff, because that's where most of the fun is. If it was just song data it could get boring pretty quick. The fun stuff is what will keep people coming back. In fact, I think "Trivia" should be a standard part of your templates...
For live gigs, I don't see any harm in allowing those pages to be made. I can imagine data that's only appropriate for Mike's database, but I can also imagine data that's more suited for a wiki. Gigs can have trivia too! (The mixing desk cut out during Jumbo... etc). Even if it's only the "tour" page, and the individual gig pages are missing because nobody wants to fill them out, who cares?
As far as the domain name goes, either underworldwiki or uwiki (with one W), nice and short.
Again, nice job; you rock.
Whenever it's ready, I want a login too!