There’s been a lot of discussion in the blogosphere about that preaching to the choir attitude, specifically leveled at UK SitP entities.
Steven Novella from Skeptics Guide to the Universe podcast and Neurologica blog (neither of which I have URLs handy for at the moment) countered it very thoughtfully.
Summarizing (liberally, and probably tainted with my own point of view) these meetings are important. They build community (if not a unified movement) and they recognize that not everyone is at the same point in the journey that is skepticism.
Not only does it provide a place to discuss topics of interest and importance, it allows people to expand their knowledge, and it provides a starting point for others.
If this weren’t basic human nature, would there be churches or professional organizations? Surely a significant portion of what they do is to cement community and promote their core principals amongst themselves. No one really questions their utility, and when it is questioned, the answer comes back: they do have value.