I think it was Ansel Adams who said, "There's nothing worse than a great print of a weak concept." This is what it really comes down to -- a strong image can be printed in a lot of different ways (e.g. the earlier reference to "Moonrise") and all of them willbe perceived as good if the image itself is strong. A weak image, on the other hand, will not be improved with a "perfect print," although many photographers out there try to do just that.
For me, the ideal print quality is one that communicates information in all areas, or at least in all important areas. That is mainly a function of contrast and exposure, ensuring that there is adequate information in all shadows and highlights. After that, there is a certain "artistic" element that comes into play. At this point, the printer tries to make a print that "sings" or a "glows" or "has light coming out of it," to use several common expressions. A difference of one second on a 23 second exposure can make or break the print at this point, as can 5 seconds of more or less development.
Salgado does not do his own prints, nor do many other well-known photographers. But then their images are so strong that pretty much any print of their negs banged out by a kid in his first 10 minutes in the darkroom will probably be decent! At the same time, though, we see photographers slaving for hours trying to squeeze the "perfect print" out of a negative that isn't worth the time of day.
It is far more important to put one's time and effort into making negatives that are worth printing than it is to spend hours printing negatives that are hardly worth seeing. With a good negative of a strong image in hand, making a "good" print is a piece of cake, fairly mechanical in fact.