A 'cachet' is a quality that distinguishes something as unique, and it connotes a state of superiority.
A "railfan's cachet" is a quality that distinguishes something as unique, and it also connotes a state of superiority--but only from the point of view of the trackside enthusiast. Everyone else regards this same thing with a state of total aversion.
Okay... so I may have just made that up... But, it kind of describes our world, doesn't it? The things that are attractive to railfans are often the very same things that others view with antipathy.
Take for example Utah Railway's (UTR) roster of Alco locomotives. No career railroader would claim that, by the late 1970s, the UTR fleet of RSD-4 and 5s was a mark of superior distinction among railroads. No, they were derided by crews for what they were: second-hand, temperamental, smokey and old. And, the railroad operated them well beyond its peers--up until 1982. But of course, for railfans, the Alco fleet was Utah Railway's cachet--it was a railfan's cachet.
Watch the video below. It is probably worth it.