In Galaxy, it took sixty Power Stars (and some Grand Stars, though those weren't as necessary -- can't you actually beat the game with only three or four of them?) to fly the Observatory to the center of the universe in a negligible amount of time (it looked to be only a few minutes, maybe a few days at most, but even ten years would be incredibly fast for a trip like that). Bowser flew Peach's castle and all his airships there too, apparently using the 120 Power Stars in the castle (the best explanation, beyond sheer dramatic effect, for why he took the whole castle instead of just kidnapping Peach), so the castle's stars are at least about half as powerful as the Power Stars scattered across the universe, and are probably the same thing. So if one single Power Star is enough to travel 1/60th of the way across the universe, how much power did it take Bowser to seal those doors in Mario 64? Apparently a lot.