Are you paying for meals or credits? Sounds like some restaurants are more expensive, so why wouldn't everyone just get a plan and go to the most expensive meal every time?
It's just me, my wife, a 6 year old girl, and a 2 year old boy going. Would every person need a plan? There's no way the kids would eat what they're paying for every meal.
Every person in the room over the age of 3 needs the same dining plan. The 2yo is no charge, as long as they share plates with someone else, if you need to order them their own meal, that you have to pay for out of pocket.
You are paying for credits, but each credit is applied towards a course, not a dollar value. So each meal includes an entree, so you can order anything that the restaurant has listed as an entree (as a general rule of thumb). There are people that do indeed order the most expensive meal every time. However, typically that is the only way to come out ahead of the dining plan. Look at the QSDP. It currently costs an adult $41.99 per night. That includes two QS meals, and one snack per day (plus one refillable mug per person). If you go to MK, the most expensive QS meal that I know of might be lunch at BOG. $13.49 for the tuna nicoise, $4.19 for a cupcake, and $2.99 for a soda. Thats $20.67 for what I believe is the most expensive CS meal in MK. So you then do dinner at Columbia Harbor House, $10.99 for the Seafood Mac & Cheese, $3.99 for the chocolate cake, and $3.19 for soda. Thats $18.17 for dinner, totaling $38.84 for the two meals. Figuring $5.19 for the most expensive snack, your total is $44.03. So in that case, yes you would save $2.04 for the day. However, if you only wanted the Croque Monsieur at BOG, that's only $11.49, so suddenly you are only saving 4 cents on the day. And if you wanted the lobster roll at CHH, that's only $10.49, so now Disney is making 46 cents off of you. If you want a Mickey bar, thats only $4.00 for the snack, so another $1.19 in profit for disney.
Similar numbers apply for the DDP, which is one CS and 1 TS per day and currently costs $60.64 per adult. Sticking with that meal at BOG at $20.67, your $5.19 snack, and then doing dinner at Crystal Palace (range of $37.99-$43.66) you would end up saving anywhere from $3.21 to $8.88. But if you didn't want to do a character meal/buffet, and went to Tony's, had the tenderloin for $23.99, chocolate cake for $5.99 and soda for $2.99, thats only $32.97, so $20.67+$5.19+$32.97, thats $58.83. so you once again end up losing $1.81.
This is why you need to run all the numbers for what you would eat and compare them to what the plan would cost you. We can post tons of ways to save money on the dining plan, and tons of ways to lose money on the dining plan.