Yeah, It is a decent perk. I do wish the waterparks were open a little later, becuase you might not get that much time. That's why I like departure day - If I have a 6 PM flight, I have time to check out of my room, go to the water park at open, stay a while, the get going. I usually pack light so I get a big locker and store my stuff, but you could just as well leave it with luggage services at your resort.
The one trick though is to make sure to find a sunny spot to dry off as much as possible so you don't have to pack a wet swimsuit. Still, a plastic bag will work for that too.