I have a slightly different take. I believe that 'cleaning marks' or 'swirl marks' etc DO affect photograph quality. The question is simply to what degree do they affect it? <Snip> Bill Mattocks
I tend to agree with Bill on this. While the degredation of the image may be so slight as to defy detection by the naked eye, I believe it's still there.
Having said that, I own two lenses that have somewhat heavy cleaning marks on the front elements and yet take seemingly beautiful pictures. One is a Nikkor LTM 50mm lens that came on a Tower RF camera sold by Sears. I bought the camera and lens from a pawn shop sometime between 1968 and 1971. The other is a more recent purchase (2004) of a 50mm f/1.5 Summarit in M-Mount. The Summarit arrived with a Leitz protective filter on it but the front lens element appears to have been cleaned with sand. Both lenses perform well so go figure!
Walker