These days, they be a far cry from the museum quality models that some companies put out. Back in the day, most of them were fine, for what they were-plastic, not brass, but that's a whole other discussion. Over the years, I did some upgrades, in terms of wheelsets, and couplers, to 'improve the cars a bit, in terms of realism (couplers) as well as functionality(being able to couple to other cars with Kadee's, as well as running better).
I think that many of these cars could still be of great utility for a number of modelers, depending upon how big their layout and collection of freight cars are, as well as how much they have to spend, etc. Some AHM cars were of a very particular prototype car, which no one's made of model of, before or since, that you can find, as easily. In a different case, which would you rather have, a Tyco or an AHM 40's gondola, vs and Athearn blue box 40' gondola?
Many of the ones that are still in my collection, may stay as part of it a while longer, unless something else comes along, which I can replace it with, for not much money, with more detail, etc. Otherwise, I expect it to remain 'in service' a while longer.