So, i didn't read the thread, but here is my experience. We are a family of 5, with 3 little girls. We went to WDW last when DDs 1&2 were 2.5 and 6. We considered not doing the DDP for the trip we are taking in June and like you said, it would save us a ton to avoid TS and stick with the cheaper CS meals. However, if we decide to go to TS meals, the DDP makes is abundantly worth our while. However, as you also said, there is a non financial Disney magic issue that is too hard to factor in with just a paper and pen.
For what its worth, we did decide to do the DDP because we really do like having that hour+ to sit in the AC and cool off and relax, as well as to meet some characters. Our TS meals are Hollywood and Vine, CRT, BOG, T-Rex, etc. we really enjoy the benefits of not only resting, but also getting some of our characters out of the way. Our girls really enjoy the not rushed opportunity to spend time with the princesses as well as the fab 5, and the food is honestly just better than CS. We also do not do a mid day break at the resort, we just feel like we lose sooooo much park time that way, between waiting for a bus, travel time, getting to the room, getting ready for a nap and then napping, and then turning around and doing it all backwards to get back to a park. Its just too hard for us.
YMMV, of course, but we find that TS break to be enough to recharge, especially for our eldest, who is closest to your girls' ages. Honestly, we find an opportunity to sit down and eat a cupcake or an ice cream cone as an adequate opportunity, which like you said, when on the DDP, you dont have to be so stingy with the snacks. Between the TS and the added snacks, we enjoy the fact that it kind of MAKES us take a few minutes to sit down and reset. We also stay 9 days, so i know how those long trips feel, and we really find that having something other than chicken nuggets or hamburgers for the adults and ambiance that is conducive and interesting to kids makes for a much more relaxing meal experience than the rushed feel we get at the tables in most CS spots....