If you plan on going to the water parks twice or more in a year, get the water parks annual pass. If you go to either water park and Disney Quest more than twice in a year, then I would upgrade my annual pass to the Premium Annual Pass.
DVC Annual Pass is $419 and the Premium Annual Pass is $524. Price difference is $105.
One day water park admission is $52.19 and DVC members get $4 off, so $48.19. Disney Quest is $45.80 and DVC members get $4.58 off, so $41.22.
Two water park days is $96.38. A water park and Disney Quest day is $89.41. Two Disney Quest days is $82.44.
For $105, on top of your annual pass, you get unlimited admission to the water parks and Disney Quest. Also the PAP discount at most merchandise locations is 20% instead of the regular AP discount of 10%.