Have to agree to disagree on that, Simon.
I have ridden the original, unfaired, K100, as well as the K75C, K75S & K1100RS at the dealer launches, plus I owned a K100RT & they do nothing for me. The XJ900S I owned a few years after the KRT was a far better bike than the BMW in pretty well all respects IMO. The last K I rode was the K75S - a test ride with a view to purchase, which I didn't as it had harsh suspension, wooden brakes & a seat like a plank. I had my KRT for all of 10 months before I shifted it - yes it was capable, with a "Comfort" seat it was comfortable, but it was also dull beyond belief with too many annoyances. To each his own, I guess.
I don't recall suggesting that the Ks were not capable bikes, typical (or maybe a bit better than others) of their time, but they do not seem to be lasting well - by which I mean they are not seen as desirable & seem to have largely disappeared from the roads in short order. Which, to get back on topic, is also what appears to be happening to the early Oilheads. I suspect that potential buyers who do a bit of research see them as potential (deep !) money pits & steer well clear - why else do you see so few on the roads ?