I would say 2 or 3, but I would really like to see the format changed to something like a round robin in pools then elimination rounds. My reasoning is that a format that guarantees more then 1 bout will be more fun for the guys like me who aren't likely to ever make it past round one in the current single elimination format.
I realize that a format like I suggest would be far more complicated, which is why I think twice a year would be good... Three times a year would be great.