To say that a fine top is ruined by mediocre quilting sounds kind of harsh to me. The bare bones function of quilting is to secure the three layers together, so if a fine top is secured to the other layers by less than optimal quilting, I'd call that 'finished,' not ruined, even though it might not be all that it could be artistically.
I notice in my quilting magazine reporting on shows, that they do have lots of judging categories, so that a hand quilted quilt is not up against a machine quilted, etc., but I guess that might not be the case in a smaller venue like a local show or county fair.