Actually I did the hiring (staffing) for several big companies (including Honeywell) for a number of years, so I know a lot about recruiting and selection. I would love to participate as a student interviewer and hope to get to do it.
I think that a student may be more perceptive to see if the candidate they are interviewing may be a good "fit". I think that is the main reason why some schools use student interviewers. I would hope that schools chose carefully who these students interviewers are and that they get some training on this. I know my friend at Louisville said the school choses carefully who they want as interviewers, so I'm surprised by what the OP said.
I only had one student interviewer in all my interviews and she was accompanied by a staff memeber, so she wasn't all by herself. I felt her questions were very well put together and when I asked her something, she was very articulate and very receptive to what I was saying. Overall I was impressed by the "caliber" of student she was and enjoyed her having as student interviewer. Actually at Louisville, both my interviewers were extremely tough, both started questioning all my "flaws" right away, but since I was already accepted at at couple of schools at the time of my interview, I didn't mind answering "straight up" and being assertive with my answers, so I had a sort of confidence that I believe I would lack had I not been accepted already. I also strongly believe this "confidence" I possessed during my interview got my an acceptance, I truly believe so. Sorry to get off tangent...