Hello, Michael,
Congratulations on planning your first Walt Disney World trip! All the decisions can certainly be overwhelming, especially dining decisions. From what you described, I don't think the
Disney Dining Plan would be a good investment for your family since it is necessary that everyone on your reservation purchase it. With your wife and daughter being light eaters, I don't think they'd order enough food to equal the dollar amount you paid for the program.
To help you specifically decide about the Quick Service Dining Plan, I would select a couple of quick service restaurants and look over the menus and have each family member "pretend order lunch and dinner" (I'm linking you to the menus of
Pecos Bill and
Columbia Harbour House as examples). Each adult would order an entree, non-alcoholic drink (if not part of the entree combo), and dessert. Your daughter would order off the children's menu. Each person will also receive a snack a day and a refillable mug. Will you have ordered at least $89.48 (the daily cost of the plan for 2 adults and 1 child; subject to change, however)? If so, it may be worthwhile. If not, I'd pass on the plan and just pay for your meals as you dine.
I hope this helps with your planning; please let us know if you have any further questions.