I went Monday night, but rode the bus from Disney Springs. I got on a bus right away, so I didn't find that annoying. However, I too wondered about parking at TL, as there were still a lot of cars in the parking lot when we left at 7:30. That indicates to me that many people drove to the water park instead of taking the bus. It's possible though those people came before the park officially closed, and then just stayed over for the AP event. I don't know though if there was anything, or anyone, actually preventing you from parking there.