Interviews take place outside the interview room as much as in. Many folks forget that they're interviewing from the moment they arrive (and if you're traveling to the interview where others can see you, you've already arrived) until the moment you leave.
I've experienced interviews that lasted up to three weeks, where we were placed together and watched. We weren't given tests and panel discussions and asked a lot of questions...just observed. The employer observed how we acted when we thought no one was watching us. We were warned early on by someone on the way out...he said "consider everything an interview." He was right. The same applies during a one-day interview...how you interact with others at the interview, how you conduct yourself at lunch, at the hotel, on the way to the interview location...all important, and you should always assume that you're being observed.
I attended an interview years ago in which a number of us stayed at the same hotel, and caught the hotel shuttle to the interview location in the morning. I later learned that the driver of the van, who overheard a lot of discussion among the interviewees, was an employee of the company, and listened intently to everything we said. A lot of was said on the van ride over, personalities showed, and the gaurd was down. People did not realize they were being watched.
Employers may be watching in the lobby, may be watching at the bar the evening before. The people you meet who appear to be interviewing may be employees who are watching you. Some companies do this; watching someone outside the formal interview setting is a much better way to gauge character, and I've see it before.
With respect to wearing your uniform, there's nothing wrong with that. My personal preference would be not, but so long as you are respectable and professional when you arrive, you're fine. You're correct to not wish to wear your interview suit...save that for the interview. I like to travel to the interview in a shirt and tie, usually a little less formal, with slacks or dockers. You're not expected to be dressed to the hilt while enroute to the interview...all you need to be is conservative and professional. Be comfortable, because your comfort level is more important than your attire. There is such a thing as over dressing for the wrong occasion.