We rarely use the quick service credit for breakfast...the snacks are more than enough. Save quick service for lunch, and table service for supper. That said, we usually do one of the breakfast buffets just once, and use the table service for it, then snack for lunch (we're usually not even hungry until 2 or 3pm after the breakfast buffet), then the quick service for supper.
The meal plan is wonderful. The portions are always ridiculous. We always end up with leftover meal credits on the last day and either end up buying a bunch of snacks (granola bars, bananas, etc.) to take home or hang around the lineup and pay for others guests' meals when they try to use cash.