I think River Country was a nice place because it wasn't the same as the other two parks. It had a different atmosphere and arguably a different purpose. Of course it was still a water park, but it was more "low key" and relaxed compared to the other two.
I don't think there's any chance of them rebuilding it but I'd visit if they did! I will say I think they should add a third water park again, even though it would most likely be much more like Blizzard Beach and less like River Country.