If you plan on pursuing academic medicine in the future, I highly recommend doing research. I'll probably stay at my school an extra year just to do research. However, I doubt that lack of research will really affect your chances of admission at most schools. There are many different way to set yourself apart from the rest of the premeds out there. Did you have any other extra-curricular interests while in undergrad? What else did you do besides volunteering at your local hospital? From my experience, it's usually better to do activities that thousands of other premeds won't have on their application (that's why I'm not volunteering at a local hospital). Also, any leadership positions in activities will also be looked upon favorably.