The belly flop from the palm tree was from directly above the pool, and he just dropped spread-eagled straight down. The next shot shows him hitting the water but clearly from a trajectory that originated from the side of the pool, and not 20 feet up in a palm tree.
Adam is watching the wet Tee Shirt contest in the front row and is completely soaked. He then is convinced to enter the men's "He Shirt" competition. When he is on stage moments later his hair is styled and dry and reacts to the water like he wasn't completely soaked already.
None of Nelson's advice to Susie on how to play Galaga has anything to do with the real-life video game. The classic Galaga did not feature thrusters, shields, pulsars, photon blasts, hyperspace, or gamma darts.
The man in the elevator who checks out Nelson stays on when Nelson and Susie get off. Later, when Nelson is looking for Susie's room, he accidentally finds the room of the man from the elevator. According to the two room numbers, they are on the same floor. If this is true, the man should have gotten off the elevator with the other two.
It is never mentioned why Ernest Dalby would have any interest in closing down the Breeze 'n' Seas Motel, though he is paying the bribe to do so.