If a water park appeals to you, then go for it!
My little suggestion - assuming you are going in the next 6 months- is to watch for cool/foul weather. Some folks will swim in any weather, but there's a reason WDW only has one water park open all winter. If the weather dips very cool (or is otherwise extreme) periodically they close both water parks!
I suggest waiting until the last minute to buy your tickets, that way you'll have alternative options in the event the weather is uncooperative.
When we have non-park days, we pick often from the following: swim at hotel, tour WDW hotels, Disney Springs (though it easily ends up costing more than other options). You could also try bowling, a movie or mini-golf.
Touring WDW hotels can include lots of fun options: free shuttle boats, a surrey bike at the BWK, walking the grounds, listening to music at GF, see horses at Ft. Wilderness, see the animals at AKL. If you are going when the holiday decorations are up, there's a ton of them to see! Even non-holidays, there's much to see at all the resorts. AoA has fun Disney character theming/décor all year round, and many resorts have very nice walking paths.
