For the 6-year programs it is (obviously) a bit of overkill, since they accept people directly out of high school.
For the 4/5-year graduate programs, it can't hurt... but the only way to get each school's take on that is to contact the schools themselves. Their individual criteria (and value on a graduate degree) could vary considerably. It's certainly worth emailing/calling all of the schools on your list.
"To array a man's will against his sickness is the supreme art of medicine."
- Henry Ward Beecher