Our local Amtrak (The Pere Marquette) is usally a Cabbage, 3 or 4 superliners and a loco. It is very rare that we see the private varnish, and it seems like most of the time we do, it is either coming to or going from the shortline I work for. Private car storage is kind of a big thing for us. We had the ex-NYC Babbling Brook until recently, and the famous NAVY observation car has been known to park on one of our sidings before.
I used to love seeing the cross-country runs through Northern Indiana with all the baggage, mail and express cars outnumbering coaches and sleepers 3 to 1. I do get to see the 110 mph Porter, IN-Kalamazoo, MI runs on occasion, but they go so fast that you can't really see them unless you catch one at a station stop.
What happened was the roadrailers were no different then the baggage cars. They would of been better off using snail mail in specialized mail cars so the railroads could at least prioritize them. The reason Triple Crown still exists is because they transport a lot more then just some mail.. CP and NS have profited from these trains which was started by NS and then expanded by Conrail and now CP rail.