While I like to indulge in a pedicure or some such when I visit home for the summer, I also bite my nails so manicures with real polish are a bit wasted on me. However, my grandfather swears by the occassional male manicure and pedicure since he's getting older and it's harder to A. reach his toes and B. keep his hands and feet maintained.
Personally, as long as your finger nails aren't dirty and you're not biting them at the interview/in the admissions office directly, I don't think it really matters. My fingernails regularly only have a tiny bit of the natural white area and sometimes none at all thanks to nervous biting and that's never held me back in any professional way that I know of. If they look jagged in a way that's noticeable, all you need to do is buy a 50 cent file and smooth them out a bit.
Since you're wearing a suit, I would stay away from really loud colors or very long (especially fake nails) just like I would stay away from a pink mohawk or really obvious (i.e. stage) make-up. While I hate how nitpicky this process is, I would hate to have to wonder why I got rejected/waitlisted and think maybe it had to do with getting an older, more traditional interviewer while wearing long nails with pink and black polka dots.