I think the first hurdle would be whether you would qualify for the DDE. Since you are not a Florida resident, you would have to be an annual passholder to even qualify.
If you are an AP holder, the DDE costs $50. You'd have to go down the lists and cross-check, but I think both discounts are pretty widely accepted. Not everywhere, certainly, but you can easily find someplace to eat on either card.
The difference between the two discounts is not just 10%. The DDE gives you 20% off,
including alcohol. For some, that is a non-benefit, but if you like a bottle of wine or a couple of beers with dinner, it's a big plus for the DDE. You will save bucks in a hurry with DDE if you eat well or drink booze.
The math would be the cost of buying ONE AP (only need one) at the
DVC discount, less whatever you were going to pay for park passes + $50. Then just calculate 10% off your food and non-alcoholic beverages vs. 20% off everything, and compare that to the cost of the DDE. YM
Will V, so you have to do your own math.