Telling musicians to evaluate and choose their instruments in a “scientific” way?

Frogman explores the issue far more eloquently than I ever could. And oh yeah... A few years back I happened to score a box of genuine tortoise shell guitar picks that had been sitting around unsold since they were still legal.  Yes, I am glad that the tortoise is no longer hunted down for its shell,  But the fact remains that not only do they truly make my steel string acoustic guitars sound better than a plastic one ever did, they reshape themselves over time to make themselves ever more comfortable to hold. 

Excellent analogy. 
Further, Gibson players don't denigrate Fender players for having inferior equipment. Effects pedal makers aren't accused of using snake oil because someone says they can't hear the effect, etc.

I'm not a guitar player but have dittled with some at the music store.  I can Feel the difference just holding and moving my hand upon one guitar from another.  Watching guitarist friends trying out different guitars.  Sound is first off.  Listening while strumming chords.  Tune it up.  But once past that they seem to be more interested in moving upon it to make music.  Kind of showoffy really.  Finger acrobatics. I can't imagine how objective science via an oscilloscope will show this.

This goes beyond guitars.  Piano, violin, clarinet...  Stereo system.  Years ago I went out to purchase a new french horn.  That horn of all horns for me. Got down to 4 manufactures/models costing between $8-12,000 at the time.  They all are fine horns as resale values represent.  Still fine horns by todays standards.  The one I purchased ultimately was because it was the most Friendly to me.  Did what I asked it to do.  Almost helping me play my best.  Objective scientific measure?  Not yet.

Devising effective tests for audio equipment SQ is child's play compared with doing it for the violin.  Every piece of wood is different.  MDF that most box speakers are made from is pretty much homogeneous.

However we still await a comprehensive suite of tests that can fully explain and predict SQ in audio products.  Perhaps even wire.  I believe we may be waiting some time.

I don’t believe it will ever happen.  I don’t believe there will ever be a time when measurements will ENTIRELY explain why audio equipment sounds the way that it does.  

Sound, and especially musical sounds, are incredibly complex and are subject to the effects of resonances to a degree usually under estimated; and an object’s resonance characteristics are changed by the tiniest changes in the physical dimensions, shape and make up of the object.  Case in point:

One of the most coveted pieces of equipment in the professional woodwind world is one of the great vintage mouthpieces (holds the reed).  It has been tried countless times, and one would think that with all of the very sophisticated modern analysis, measuring tools and techniques that are available to modern manufactures that a great mouthpiece could be created that closely, if not entirely, duplicates the playing characteristics and sound of these vintage pieces.  Hasn’t happened yet.  Of course the same can be said as concerns the instruments themselves.  There is great modern gear available to be sure, but for players seeking a certain sound and playability characteristics, the vintage route is often the only way.

I will leave to others the possible reasons why and how the effects of resonance impact musical sound when it is being transmitted in the electrical domain as is the case with audio equipment.  However, it is clear to me that it does based on the effects of the many related tweaks that we play around with as audiophiles.  So, it all leads me to the conclusion that there is much more going on in this area in ways that are not as obvious nor accessible.