I am very ashamed to admit how many brain cells I have wasted on these calculations, but here are my thoughts
We usually get the
DDP because my DH loves to try all of the different TS restaurants. I think it's way too much food, and we usually are trying to blow snack credits the last day. So what I did to convince him that it is not worth it is I looked at all of the menus of the restaurants where we usually like to eat and I priced the separate items that I thought we were likely to order, being extremely generous. We saved several hundred dollars by not doing the DDP, and that is NOT sharing meals or doing things like that that I normally do. I found that the only way to come out ahead with the DDP is if you eat at the more expensive restaurants and you choose the most expensive things on the menu, in addition to the desserts. So, it only worked out for us on days when we do the buffets like Boma or O'Hana, and then we're really only getting the snack for free, so it's not that much of a savings. Since we're DVC, we can do split stays, and I'll get the DDP for just two days or so and have the ADRs for those places on the days that we have DDP. Although I have never done the QSDP, if you have several children, it actually may save quite a bit for you because they are so cheap on that plan... and you get two snacks a day which is awesome, I love Disney's snacks more than the meals!
So, if you do not typically order the most expensive things at the most expensive restaurants, or do not order dessert with every meal, or snack alot, then you will definitely come out ahead paying with cash or using the prepaid card. If you do really want to splurge, and everyone should on vacation when they can afford it, then definitely go for the DDP... there is also something to be said for that psychological freedom of being able to say "yes" to everything, and for some people that's priceless!