If you're wearing a jacket and tie and don't get the job, I sincerely doubt it was because of your attire. In the end with all other things being equal, your attitude and personality will win the day. If you project ease, confidence, and humility (admittedly a difficult thing to pull off), a lot of doors open up.
Very well put.
As an engineering recruiter of eight years, here is my take on interview attire:
1. Stick to the basics: You can rarely go wrong with charcoal/navy suit, paired with white/light blue shirt, black oxfords, and dark, solid tie. If in doubt, ask the recruiter before you go on your onsite interview.
2. Perfectly acceptable alternative: Navy blazer, grey trousers, black/dark brown oxfords, navy/red/black solid tie.
3. If you are meeting with a C, D, VP, and/or President level executive, wear a suit. This is a sign of respect both to the person and his/her executive office, that is granting you their time and opportunity.
4. If you are visiting a plant or shop floor as part of the interview, ask the hiring manager or recruiter about suggested attire when they contact you to schedule that in-person visit. You may have to wear protective gear, and will most likely be asked to wear comfortable clothing. In such cases, chinos, button down shirt, and semi-casual shoes/boots might work best.
As Snow Hill Pond stated, your skills, personality, and attitude are what will ultimately get you the job.
Good luck.