For us, it is a combination of both convenience and savings.
Would we eat as many sit down meals without the meal plan? Probably not. But, in the past we have always done two or three day commando-style vacations, and we were always very concerned about prices and time spent eating. This year we are finally going for a full week (Woo hoo!!!) and we want to fully enjoy all Disney has to offer- including more Table Service dining.
We crunched the numbers, and if we compared meal-to-meal, we absolutely save $$$. We even compared how we usually eat ( counter svc lunch, table svc dinners one out of every three days, counter svc most often) and we STILL come out about even!
So, we are doing the Dining plan. We will enjoy the convenience of having the meals prepaid. We will also love not worrying about how much to spend- or not spend- on what we want to order at restaurants. Plus, having tax and tip taken care of is great, too! Sometimes that can add a lot onto the budget.