Very rarely are you actually lifting the weight of the board with your legs. Going off a kicker launches you up, and when you go to do a grab you're not lifting the board up to you, you're compressing in the air (ie. your head and shoulders actually go down, lower legs and board come up). I understand a lighter board will potentially be easier for spins, but we're talking marginal differences here. I'd get something that fits well that you ride comfortably on.
I would take a super poppy slightly heavier board, than a wet noodle light board any day.