Results: around 12 respondents; one 17, one 18, one who'd never written lyrics but said he might like to, a few random ones that I didn't like for various reasons, and a host of singer/guitarists. I play guitar. Another guitarist is not the optimal fit here, and just about any other instrument would do.
All male. Despite the list of bands I listed, most of them didn't indicate anything about bands they liked or what genre of rock they'd like. Three of them provided links to previous music they'd recorded; the other nine had no recorded music, and didn't want to send written samples of lyrics so I could actually have some basis to make a decision.
I'm still in contact with three of them, but I think I'm just going to punt it. The person I'd want to work with probably isn't looking on craigslist for a cowriter. Well, one of the guys was pretty interesting and liked the song I'd posted, but he was looking for success in the music business, and to me it's just a hobby.
(I did find my apartment through craigslist a year ago, so it's not all bad.)