I definitely agree with the "start small" approach. We (1540) host two off-season events: BunnyBots (
http://team1540.org/bunnybots) and Girls Generation (
http://team1540.org/girlsgeneration). BunnyBots is more of a mini-build season with its own robots, different games each year, and around 25 teams participating. It's a great way to get new members up to speed for build season. Girls Generation (as the name may suggest), is an all-girls event played with the previous season's robots. It's a great way to get girls on the drive team (something that historically has not been the case in competition) and boys into outreach roles (we run the event, since all the girls are busy). Both of these are one-day affairs (load-in can be the night before, but whatever), and are fantastic for everyone involved. Message me or email
robotics@catlin.edu if you want to get one of these started in your area.