The QS dining plan (or any dining plan) really doesn't save you money, it's more of a convenience thing because you have all of your meals paid for in advance so don't really need to worry that part while on vacation. That said if you typically eat a meal including dessert at each x everyone in your family it's worth considering.
For our family it's not worth it at all. First my kids aren't big on the selection of kids meals and prefer to split an adult meal or do some variation of what's on the menu. Secondly we don't eat dessert with every meal, or if we did get dessert we would tend to share because we just wanted a bite. Several desserts at a single meal would be wasted on us.
If you like the thought of prepaying but don't want to be limited to the requirements of the dining plan you could always put the funds onto a prepaid visa or Disney gift card. This way when your trip is over if you have left over funds they are yours to use elsewhere and you don't end up with 18 snack credits and bringing home a pile of mickey rice crispy treats.
Also considering your in a family suite and have access to a fridge, it would probably be worthwhile to plan on some breakfasts in your room. Cereal is quick and easy and you will get to the park a lot faster each morning not having to make stops for breakfast. Not to mention the savings.
FWIW, I do think the refillable mugs are worth it if your a soda drinker and close enough to the food court that it's not out of your way to go refill.