How much can be measured -- and how much cannot?

Emotions and logic are two different contexts. Perhaps both are needed to fully evaluate and appreciate equipment and systems. For music, the final evaluation is how much is emotionally moving to the listener. One can ask, "do I hear detail, staging, extension, depth and evenness of frequency response," but in the end, whether any of these characteristics is emotionally involving is the ultimate question and challenge, and for that, to my knowledge, no quantitative measurement has been, so far, predictive.

"The number of times that I and many others have referred to John Atkinson's measurements in helping Audiogon members to make purchase decisions or to diagnose problems is practically countless."
Actually I have never found measurements to help me in any audio decision to by a certain product. Measurements are helpful in the design process but do not tell you anything how a component will sound. Use your ears and they will guide you on the right path

If we spent more time listening than thinking we would be better off.

And I will add that learning to read and understand measurements will provide a great education to an audiophile. When I compare the specs I looked at originally compared to the factors that I try to take into account now, I realize how much I have learned from this hobby.

Off the top of my head, factors that I now take into account:
output voltage
output impedance
input impedance
input sensitivity
gain
harmonics distortion (2nd, 3rd order, etc)
damping factor
speaker distortion (hard to find in general)
crossover point
crossover slope (1st, 2nd, 4th order etc.)

I'd also add to that list the standard plots vs. frequency graphs that one sees in Stereophile's measurements section.

And when I see many of Al and others' posts, I realize that there is much more to learn.

BUT all of that having been said, I too ultimately come down on the side of letting your ears make the final decision. Psychoacoustics are pretty wild, can be tough to get your head around, and aspects of them are difficult/impossible to measure. Heck there are very likely aspects to psychoacoustics that remain to be identified. But trust your ears, they are excellent psychoacoustic instruments connected to all the bits of the brain that matter for a satisfying experience of music.