I have never, not once, spent as much just ordering what I wanted as the equivalent dining plan would have cost. And this goes back to the very earliest days of the plan. Usually, that's becuase I have the "wrong number" of sit-down meals, and almost never average exactly one or two per day.
But, even then, we don't order the way the plan wants me to order. For example, sometimes one of us isn't that hungry, and wants to make a meal out of a salad and an app. Or I want an entree (or a restaurant) that is a bad value on the Plan. Or we want apps but not dessert. Or we want dessert, but later. Or, or, or...
Could I make the plan work for me? Yes, if I ordered with that as a goal. But then I'm ordering to make the plan price out, and not ordering what I actually want to eat.