I am pretty into the skeptic community and i do wish more people had heard of less wrong. I think it would be a great idea to try to make an outreach effort to those groups. For instance the skeptics usually want to improve their rationality (the other groups you list might). I know the biggest skeptic podcast talks about things related to rationality quite often. Although I am pretty disappointed at the lack of knowledge of bias, heuristics and things like bayes theorem amongst the people who i have talked to in the skeptics community
At Balticon, there was a table for humanists, the Ethical Society, and skeptics. I told one of the folks there about Less Wrong-- he seemed interested and I'll check back with him, but he'd never heard of it at all-- it took a little time to disambiguate between Less Wrong and what he heard as a human being named Les Wrong.
Anyway, what do you think of doing outreach to fairly compatible groups (I'd add Unitarians to the list)? And if so, what would be good methods?