I would conjecture that the je ne sais quoi quality of lenses is most apparent to photographers who have never looked through them to see the actual image. Users of rangefinder cameras (and to a lesser extent 35mm SLR's) must get continual surprises, good and bad, when the photographs they get don't match what they saw through the viewfinder. In my experience with view cameras where every aspect of image structure is available for detailed inspection in advance of exposure there is no je ne sais quoi quality at all.