The 4th week is great! The parks got pretty busy on Sat because of the Labor Day weekend. Other than the weekend, the lines were minimal and we were able to "wing it". We were able to walk on to most restaurants without a PS. In fact, we booked a PS on CRT the same week we were there.
The only negative is - it's very hot and humid in August, and thunderstorms are common in the afternoon. We didn't mind the thunderstorms coz they were short-lived and brought the temperature down.
If you love waterparks, this would be the ideal time to go.
Have fun planning your trip!