If you haven't yet read Fred Pohl's Gateway, you should do so immediately. If you need more convincing than that, you should head over to Tor.com and read Jo Walton's amazing three-and-a-half-decades-after-the-fact review of the book. And then you should read Gateway.
It's my opinion that, in general, the human race produces better art as time goes on. And I don't think genre fiction is any exception. This is, to be honest, a big part of the reason why I feel so strongly that a healthy periodical market for science fiction is crucial. After all, the old masters were quite prolific. There is a lifetime of reading in the accepted genre classics alone.
And I do think that fans should read the classics. To get a sense of history if nothing else (you damn kids). More than that, science fiction, like all literature, is a sort of ongoing meta-conversation. Recent books are better enjoyed within the context of the works that came before. Without the context it's like you've joined the dialogue mid-sentence.
That said, there's not a doubt in my mind that the great writer's of today are producing fiction that is simply better than that that was being written thirty-five or seventy years ago. But there are some books that stand out, that lose not an iota of their lustre with each passing year. Gateway is one of those books, and I thank Jo Walton for reminding me to reread it.