DH & I had the regular
DDP several times. I kept receipts to keep track of the actual cash cost of the food we ate...would have been $619.45 cash for 6 nights. DDP cost then (2008) was $455.88...savings of $163 for us. We have had similar savings each time
That said, we tend towards the "maximise" end of the scale. All our table service credits are used at dinner - which is the most expensive meals on site of course. We don't do many buffets (or none.) Buffets tend to be less expensive than menu meals - like a set price of $28 when a menu restaurant would more typically run in the $35-$50 per person range. We really like the high-end items on the menus -- would usually tend to order the higher-priced entrees like steaks instead of cheaper pasta dishes for example. We do like dessert, and do order it when on vacation.
all of our counter service meals were at lunch -- again, a better value for your DDP credit since lunch is more expensive than breakfast. And again, we tend to like higher priced lunch items too. If you go with your burger/fries type meal, you're in the $8-10 range for lunch. But we went for things like the $14 ribs platter at Flame Tree, or the $15 shwarma platter at Morocco/Epcot.
We always felt quite full on the DDP - to the point we rarely wanted snacks after the first day. We had taken cereal bars & poptarts for breakfast in the room, but since we weren't using our snack credits in the parks, we started buying pastries in the various bakeries & taking them back to the room for next day's breakfast.
Now, if your group wants to have a big hot breakfast everyday...or if you'd prefer buffets for dinner & burgers/fries for lunch, you might just price out the cash cost cuz it might be cheaper to just pay as you go. Similarly, if you tend to prefer the chicken or pasta entrees...and you wouldn't want dessert it would probably be cheaper to pay cash. You just have to look over the menus of the places your group might want to eat at...and crunch the numbers some to find what'd work best for you.