Jennifer, I like that "just friends housed together."
If Getaway attendees all joined FSGW, we'd really throw a spanner in the works. Heck, it doesn't cost anything extra when you figure the membership fee is deducted from the cost of the Getaway, plus we get the wonderful newsletter which tells us about all the stuff we're missing because we're not local! I haven't done this, because it means someone will have to print and send a newsletter to me every year. It means I may be asked to vote for FSGW officers. I wouldn't do that, because I don't know them well enough - I'd leave it up to local folks who knew what nominees were about.
What say FSGW members?
One note on drawing quiet folks into a group - don't try it! I'm a not-shy person with a lack of confidence. Truly shy people can be very confident about certain things, but are uncomfortable with interpersonal communication with people they don't know.
There's nothing scarier for both types of corner-sitters than to try to drag them somewhere they don't want to be. Sure, invite them, but don't push. If they like the corner, let them stay there until they want to come out. Introduce yourself, tell people you like something they do, smile at them, but don't try to draw them into a conversation, or the next time they see you, they'll walk the other way. The point is for people to feel comfortable being who and where they want to be, and not trying to change them. The latter is about your comfort level, not theirs.