I have started a little research project wherein I have been harvesting the feeds of various Internet-active radio stations so I can look for the "deep cuts." Not just for classic rock, but for various "new wave" stations, as well as combining old "top 500" lists, and so on. I am nowhere near done, but I have made some notes that confirm old suspicions.
One, you're quite right about classic rock having a lot of deep cuts that just don't make it outside of some specific instances. On the other hand, not only was new wave not entirely congruent to the 1980s, but a lot of what gets called new wave on various stations is only music that existed in the 1980s, rather than being actual new wave. New wave was fairly tight and the rest is padding.
"Darkjazz" really came and went, and it's unfortunate. I'm still working my way through it but there was a hell of a drop-off.
Speaking of researched tracks, I think when an artist dies, there's a contraction of what of their tracks get played on air.
Another thought, this one purely math. If you bought, say, ten CDs every year, new releases, well, the average age of your collection will age at about half your own age rate. The only ways to prevent that, if this concerns you, is to either jettison your old music or gather ever-increasing amounts of new music.
All of this is to say that, unless your preference is "whatever is on the radio ... played a reasonable volume" (Pictures for Sad Children), you're swimming upstream, against the fantastically evolved. Taste gave way to faddishness, then payola, and now, well, The Algorithm. It's a fight to find what you might like rather than what is just being extruded like soft serve.