Wow - I just graduated (UH - go coogs) and no one wore suits unless there was a job fair. I never interviewed to get in, but then again you may be headed to Duke or Harvard in which case - best of luck.
My personal fave for a job, dress like the interviewer, or adopt the "normal" or most-common look you see before heading in. That way you look like you belong and the person interviewing knows that you should fit in. For safety, dress one step above what you're seeing.
To get in to school, I would try to look as though I were graduating and interviewing for a job. In a few years the school will be marketing you as a recent grad, ready for a management post somewhere in Corporate America. The more you look like you "get it" the better they will like you.
Personally I would wear the suit and keep a tie in my pocket in case someone is wearing a tie, but that betokens my cowardice and insecurity.
Once again, good luck!