If OP wants to spend 2 hours a day getting from a water park to a theme park and back (while making sure to leave the theme parks by mid-afternoon), all to "save" money on parking, then go for it.
But as for advice I would strongly echo other posters who recommended upgrading one of the ultimate park hopper passes to an AP (no need to upgrade all of them). That would probably be not much more expensive, and could possibly save further money on some meals, etc. Then parking everywhere at WDW is free. You'd just need to present the AP to the parking attendant. That way, for about the same amount of money, you get free parking.
This is the simplest, most cost effective and best logistical way to avoid parking fees. You can park at the park you're going to, and you don't have to leave at 4 or 5 to make sure you get somewhere else to pick up your car.