I was just reading the current (May 2007) issue of EQ magazine when I came across an interview with high-end microphone designer Klaus Heyne. In it, he very nicely summed up what I’ve been trying to verbalize about photography, image manipulation (be it chemical, optical, or digital), and good "straight" lens rendering in general (sharpness, macrocontrast, microcontrast, etc.). Of course he was talking about music, but it works just as well for photography:
My definition of a good mic is: the musical experience never wanders away from my pleasure center to my intellectual side, to where I might think, "Oh yeah, I can really hear the cymbals, they’re right over here. I can ear the second violinist tapping her foot." I regard that as intellectual wanking. I won’t want that. I want to be there. I don’t even want to think. I want to be in the music, so I can have the experience of dreaming and imagining, rather than analyzing how the setup is.
What I get out of it is: don’t break the spell. I’ve seen extreme manipulations that don’t and subtle ones that do, so I don’t think it’s a matter of degree, rather whether it reinforces the experience or distract from it.