We always do the DxDDP. I really like appetizers more than dessert so it is kind of a no brainer for us. For the most part we eat an early lunch and a later 2 credit signature dinner. Plus we try to spread the credits over to an extra day. We rarely actually have 3 meals. We don't always eat every course, mostly we skip desserts here & there or share one. I have never been one to worry about "maximizing" our value.
What about having TS breakfast (or early lunch) and dinner and then using some credits for QS during the day? The boys would probably like that. Especially eating around EPCOT.
Or maybe you & Mike could have a special 2 credit dinner alone while the boys watch the kids? Cali Grille is wonderful!
Or the dinner shows ... Hoop De Doo or the Luau? They are two credits. And the Castle is 2 credits.
I wouldn't worry as much about using every last credit. If you will ultimately "save" money upgrading to Deluxe, then do it. Enjoy what you can but don't force anything. I have heard that you can trade a meal credit for a few (I think 3?) snacks. Maybe you can bring treats home to prolong the magic?
Edited to add that tax is included with the plan, but yes you do need to have money for tips. I usually get gift cards that we use just for that purpose.