re: Shuttle Simply Doesn't Have Enough Power.
It's more than this. The Shuttle has wings and requires the structure strength and heat resistance to re-enter the Earth's atmosphere at around 8 km/sec (17,000 mph). Plus if the Shuttle could somehow get to Moon, and if it's going to do a direct descent to Earth surface, it needs to enter Earth atmosphere at around 25,000 mph- and it's not designed to withstand the structural and thermal load from this higher speed of entry. [You could solve this by trying to get Shuttle to first go into orbit around Earth, then re-enter; though this has never been done & has some problems to resolve. So, this is a *relatively* a minor point, compared to attempting to lift all that extra dead weight to a lunar trajectory]