Just a thought, being avid divers and Jetskiers we can extend the season by wearing sorty wetsuits, If you are inclined and determined to go to a water park. We wore shorty wetsuits many years ago and did draw some attention from some cast members regarding the zippers, however they cleared us after seeing that the zippers get covered by a velcro closure. that same trip we saw hundreds of womens and mens suits that has zippers and buttons, apparently WDW is concerned about scratching the slides, so certainly check the rules again
What some folks don't realize is that despite water temp being 80 degrees our bodies are still 98 or so dgress so there is still a considerable heat loss, I second everyones opinion, it's up to the individual but i certainly wouldn't want to blow a day on my hopper to find out it was too cold to have fun...My $.02