Music isn't scientific, it's all about feel and emotion.
Music IS largely scientific, although it can be very difficult to understand it from a scientific perspective, to the point that it can seem as if it is not scientific. I agree with you in principle though, because it is very difficult to test every last difference between a vintage instrument and another instrument, and because there is so much going on psychologically, all that really matters is what instrument you play best with, whether it is a vintage treasure, or a nice example of a modern instrument.
Not sure I agree with that - only in the sense that everything is basically physics and therefore can be measured!
There is more to it than that - musical scales are derived mathematically, and individual roles of each note (dominant, subdominant, tonic, etc.) can also be expressed mathematically. When you learn to play, even without learning the theory, but playing with a sense of 'feel', what you are really doing is learning patterns that represent the underlying mathematics, even though you are not formalising them. This is how we can build computers that can compose pretty good music - because it is largely mathematical. Also, with respect to the guitar, Physics is important because the way the pickups are wound, potted, etc. affects the tone of the instrument, and the scale length affects the sound, etc. All of these rely on principles of Physics and so should in theory be testable between a vintage and a new instrument.
Of course, there is also an art element to music too, which is why I said that music is largely scientific, not completely. This is why those computers that create music are usually no match for Clapton, or Van Halen, or whoever. You need to know what emotion you are targeting and what musical concepts will portray that well - that's where the art comes in.
TL;DR - I'm not saying that music is completely scientific, but a lot more so than most musicians usually realise.
