Hi Stephanie! The main
Ol' Man Island pool at
Port Orleans Riverside is open until around 10pm every night, subject to weather conditions. However, there are several quiet pools throughout the resort that are open 24 hours, but these pools do not have lifeguards on duty, or towels available onsite.
That said, if your family are big into water slides, wave pools and the other fun to be had at both Disney's
Typhoon Lagoon or
Blizzard Beach, I definitely think the water park option is worth it. You could very easily spend an entire day just at one of the water parks, especially in the August heat, but if you'd like to break it up by a visit to a theme park, of course you can do that too. The one common factor I've found with my kids at the water parks is once they get there, they do NOT want to leave! It's really up to how you think your family will enjoy the water parks, or be satisfied with the pool options at Riverside.
Whatever you decide, I hope you have a fabulous vacation! Let us know if you have any other questions.
~Suzannah