I find the tie quite interesting, and also believe it is a key piece of evidence for the case.
Based on the spiral aluminum chips and pure titanium particles in Cooper's tie, he probably isn't a banker, baker, carpenter, insurance agent, or a host of other professionals. If you believe the tie belonged to Cooper, and believe the Citizen Sleuth conclusions that he is an engineer in a specialized metal-working facility, then we have just drastically limited the field of suspects.
The cigarette brand he smoked, and whether or not he smoked on a regular basis, is not nearly as important as his profession and place of work.
In my book, I lean heavily on the fact that Cooper is an engineer. He is intelligent, inventive, and meticulously plans this hijacking. When you view the case from this perspective, all of the "mysteries" and conundrums are gone. We are only left with who is Dan Cooper and where is he now?