I think it really depends on the school since there are NO nationwide guidelines on what it is AED chapters should be doing. I know at Hopkins AED (admitting im the VP of AED here) organizes mentoring, tutoring, and service projects and does fundraising for itself and for charities. We also sponsor a prehealth lecture series directed at exploring careers in medicine. At Hopkins, I would consider AED a more than legitimate activity as well as an honor society.
But, I have no doubt that there are schools where you just sign up and chill out. As with all activities, if its BS at your school its not going to help you.