There's really nothing quite like building a robot, even a simple box on wheels. Here in Oregon we host the BunnyBot pre-season competition each fall. Last year's game can be seen at
http://www.oregonfirst.org/regional-...bot-scrimmage/ . This year's game comes out September 11th. For BunnyBots we invent a new, simple game to be played with FRC-class robots on Saturday Dec 18th. Students learn a ton and some say it's more fun than FRC because the pressure-to-fun ratio is more tilted towards fun and newer members have a greater role.
San Diego has such a great community of teams you could probably get something similar going down there. If that's too much to take on, just have new members build something FRC-like and drive it around the school. You'll be amazed in the difference in energy level of those folks. I'd take apart last year's robot if need be to make it happen...I'm such a big fan of having a pre-season robot project.