IMO there are 2 types of eaters at WDW. The first, Just want enough food to keep them going and "would never eat all the food they get with the dining plan". The second type feel that the restaurants are every bit of an experience as the rides are and don't want to be limited in what they do.
We fall into the second group. We always get the plan because, although a burger would fill our stomach and keep us going, it is not near as good as the dinner at O'hana or Be Our Guest. Do we always order the most expensive thing? No, not always. Do we always eat everything on our plate? Nope, hardly ever. Do we all try different things and share? You bet!! It's all an experience. Try new things, Get a bunch of deserts and try a bite or two of each, order things you normally wouldn't. Are you going to save hundreds by using the dining plan? No, but there is value to it. As another poster said, you may only save $20! But chances are with the dining plan you got all of your reservations (because you knew you needed to make them early) and you tried new things. To us this is how we get our money's worth, not by eating everything on our plate.