Check your throttle shaft(s) for excessive play every so often, and rebuild when it gets loose. Under normal conditions this takes many many years to happen. A good cleaning is always healthy, however, and I do one once a year just to keep the gunk and crap out of the carb. I use Holleys, so it is a rediculously easy task to perform on these carbs.
Well, I wouldn't rebuild it every spring, that would just be a waste of money. Definately clean it though to get rid of the gunk that builds up from sitting fuel. Sometimes rubber parts degrade from gasoline, and might need to be replaced, but a whole REBUILD is not necessary until it a lot of wear is noticed; namely in the throttle shaft(s).