Hi!
We were so uncertain whether the plan made sense that I went through and did a calculation for every day based on how we are planning to eat, assuming that we never ordered dessert at counter service unless we could get fruit and mainly used our snack credits for water, since that's our plan. I also assumed that dd10 would eat off the kids menu at many restaurants even though we have to pay for her as an adult (we also have a ds 7). I assumed that we will order appetizers and desserts at all ts, but we didn't plan our ts to maximize value, so we aren't necessarily hitting the expensive places.
Even with these assumptions and paying for dd10 as an adult the plan will save us a little over $200. The plan is costing us about $1,000 for eight nights. Last time we were at WDW, three years ago so dd was always paying kid prices, our ts and cs expenses for a seven night stay were somewhere between $800 and $900 and we ate all breakfasts and about two lunches and dinners in (we are DVC members and had a kitchen). So if we did it on our own we might save slightly off the $1,000 but we would be eating out waaay less and at way less interesting places, with everyone watching prices when they ordered.
So we decided to go with the plan! Sorry so long winded, hope this is helpful.