Thanks for sharing the article - interesting selection of pieces.
The article itself says more about the evolution in Paul Morley's musical taste(s) than about any change in classical music's relevance. Classical music was just as relevant in the 60s and 70s as it is now; Paul Morley was simply otherwise engaged at that time.
I don't think he's saying that Classical music has changed but that the world of pop has - becoming tired and trite. Nothing new there, so why not explore the challenges presented by what once may have seemed old and irrelevant and find new relevance in it. He made it clear that it's his changing personal perception.
Of course to some all this is all old news but to others it may be a push in an interesting direction out of an apparent dead end.
Personally, I like Morley – I like his imaginative writing. He can be glibly clever but he's far more incisive and insightful than most of the other people in the Guardian, or those on Newsnight Review (when I can be bothered to watch). I understand he annoys people but that's his job. I'm far more annoyed by Andrew Graham Dixon on The Culture W*** Art Show