Only you know if you would use the waterpark/PI options and how often.
A 10 day MYW pass with park hopping and waterpark/PI options plus no-expiration would cost $478.19 / adult (advance price incl tax)
A DVC discounted AP would cost $355.71 (incl tax) and a DVC-discounted PAP would cost $462.21 (incl tax).
So the ability to have 2 or 3 extra non-expiring days and the plus options costs for a future trip costs $122.48 more than the AP. (If you would normally buy the PAP, I think the 10 day wins, given your stated plans).
You are the ony one who can decide if it's worth it - we don't visit waterparks / PI very often so we'd go with the AP. But your touring habits probably differ from ours - if you use the waterparks/visit PI, getting 3 trips out of the pass may make it worth it to you.