It is always important that you set a good impression. What you wear is perhaps not as important as how you wear it. I would rather see someone who is smart and clean than someone in a Prince Charles suit that looks as if its come out of the laundry basket with creases and stains all over it. I had a great Aunt who once said you can tell most about a person by looking at their shoes! At the bottom end of the ladder its all about making an impression. I am staggered by the number of people I see these days who have no idea how to determine their shirt size, if the shirt doesn't fit, a tie will always look like an after thought. Flying instructor clobber is working attire, would you go for an engineering interview wearing a boiler suit?
I recall an RAF colleague going to Gloucester for a career interview as was the custom, the invitation letter simply said: "Civilian clothes should be worn". This guy turned up in a gaily coloured tank-top, not quite what the interviewer had expected.