Hi Laura,
The Disney Dining Quick Service meal plan is a good deal if you have young children under the age of 9. It is also a good deal if you want to be flexible with your dining options and you are okay with the repetition of the food.
I think for a normal eater the portions are fine. In some cases, there might be more food than you need. If you have a growing teenager, you might want to budget extra food:)
As for variety, there are lots of different restaurants to try. However, each park is going to have a standard option especially on the children's menu. Adults will find more variety as each restaurant has a "specialty" meal.
As for getting to a non-Disney restaurant without a car, you can not walk to one. The resorts are located in the middle a large property. You could take the bus called the Lynx but you really would not be saving that much when you add the bus cost.
To save on meals, you can send snacks ahead or order from the Garden Grocer who will deliver food to your resort. If you are in the family suites, you will have a small kitchenette to keep you groceries.
Wishing you a magical vacation!
Beth