"Class" seems to have held up very well. I remember back when it was published trying to shoehorn myself into his "Class X". I had to squint really hard.
I think the core problem was his not recognizing Class X as just the usual bohemian avant-garde, and thinking that it represented some shift in the class hierarchy rather than a constant part of it. His hope for some bright future for this "classless" class was simply misplaced, because he didn't see what it actually was. Which makes the end of that otherwise fun book kind of a downer.