As a devotee of historical recordings, it probably goes without saying that sound quality isn't always the main factor in my choices. ;-) Taking Mozart as an example, there's a rather crusty 1955 broadcast of Walter Gieseking and Guido Cantelli performing piano concerto #21 that is, IMO, the single best performance of a Mozart concerto I've ever heard. Cantelli conducts the New York Philharmonic with tremendous gusto and Gieseking, who could play quite indifferently in his last years, delivers a sparkling performance that is simply irresistible. Similarly, there's another broadcast from the same period of PC #22 with Edwin Fischer and the Danish Chamber Orchestra that is just sublime. For Bach, I return often to Georges Enescu's recordings of the Bach Sonatas and Partitas. Some listeners can't get past his deteriorating technique and the deplorable recording, but I find them achingly beautiful. And of course there are a myriad number of great historical performances in less than modern sound that classical music lovers treasure.
OTOH, there's no shortage of beautifully recorded, exciting new artists. (A friend of mine keeps saying "They're coming out of the woodwork!") And current remastering techniques have added new lustre to classic recordings from the 60's and 70's. I was recently struck by Peter Serkin's excellent Chopin disc from 1979--I had no idea.
I think if recording quality is one's sole criterion, one is missing out on a lot of superb music. A real music lover isn't going to be deterred in this way. But it's certainly nice when the two circumstances come together. And I think bassbuyer makes a good point about sound quality being helpful when you want to explore music that is new to you.
