It will depend on where you eat (but the plan is good at all park restaurants that are owned and operated by Disney--that leaves out AK RFC) it is good in all food courts, disney hotels, and at several locations in DTD), but with the change over for adult pricing on kids 10+ for any character dining experiences you might find it worth it. One thing you might check is all ears they have the menus for each of the restaurants and you can get an idea of the pricing--you might even get the kids to split some meals and save the extra credit for signature dining. In additon, if your kids are more traditional in their CS choices you may have problems feeding them from the children's CS options--though much more healthy, they are much more limited. Again even if they share a CS for lunch you'd just have an extra CS they could split for breakfast. As for snacks--it is only 1 per person per day, so one soda or one water or one ice cream, even if you used 2 everyother day and got a popcorn and water. In addition it is good to remember that tax and tip are included. The way I figure it if we get a CS meal for about $9.00-$11.00 (combo plus dessert or entree, drink dessert), dinner for about $20-25 (appetizer, drink, entree, and dessert)and snack $2.50 after tax and tip are added it is at least a breakeven. I have a similiar scenario withthe two kids , both are considered adult by DD standards. Since I am paying for them both to eat as adults, DD and DS could share one full adult TS meal (between the appetizer, entree and dessert there would be plenty of food in many cases), I'd just save the extra credit and use it somewhere else during the vacation. I don't mind purchasing an extra drink--heck I often drink water so she could have my drink. DD also didn't like many of hte children's CS options--many places didn't have hotdogs, burgers and chicken fingers on the children's menu and there is no children's pizza at pizzafari.
If I were you I'd check the menus to be sure that the dining plan wouldn't at least be a breakeven.