Good times, good times
We've been going to Summer Waves every year for five years as part of our annual Jekyll Island trip. It isn't huge, but it has something for all three of our sons (14, 9 and 4) which is saying something. I'm reading the negative reviews and wondering what absolute fantasy world these people come from where everything is absolutely perfect all the time. Yes, bathrooms in a large public place sometimes smell, and Summer Waves is no exception, but the pools, rides and pathways have always been very clean, the staff as attentive as they should be and I have never run into an occasion of the innertubes being in short supply.
I injured myself one year, slipping and scraping my knee pretty badly, and the manager gave us five free passes so that we could come back the following year.
As for the weather, it is much like Florida in that you cannot tell when it is going to blow over in an hour or hang out all evening, so I suggest getting a two day pass (25$) and if you can use both days, great! If not, if its raining all day one day, chances are it will be alright the next. 25$ is what you pay at most theme parks for passes, afterall.
In the past, they have also had an evening pass, I think after 3pm, for 10$ a person. If they're still running that deal, its a great one. Play at the beach in the morning, take a break for lunch, have a nap, and then hit the park for less than half the price. Just keep an eye on the weather and see if that day is going to turn into a Florida-like afternoon shower or stay nice for the evening.
Would I drive two hours out of my way to go there? Probably not anymore than I would go to another city to take my kid to an art museum or park that they liked. This is something you would do because it fit into your plans.