Once, maybe. Twice, no way.
MGC has lots of vendors, some good speakers, a pinball tournament, and a museum which has lots of games.
The vendors are pretty good. Lots of good deals, but quite a few bad ones as well. Lots of people selling arcade cabinets and parts if that is your thing, too.
The museum is pretty much the same every year.
The speakers haven't been announced yet, but I would bet on Marty Goldberg and Ben Heckendorn being two of them. Ralph Baer was going to go in 2006 but he got sick and couldn't come.

I have never done the pinball tournament thing, it too expensive for my tastes. Last year there was a shoot'em'up tournament too, but since Kamino is gone I don't think there will be another one this year.
The guys from Team Fremont do a game show style trivia contest which can be fun (especially if you were selected one year like two of us Lazer Dorks were). Keranu's heckling that year in Team LD's favor was the most hilarious thing I have ever seen, even if we beefed it and lost horribly to some genius kid.
Keranu wrote articles with pictures on Lazer Dorks on the
2006 and
2007 MGC.
EDIT: God damn it, K, you beat me to it.