Xurtio

Well certainly the body and the strings resonate off each other, but it would probably be subtle in the final recording... but as the musician holding and playing the guitar, I appreciate a resonating body.

You're right about A major (I just don't play major on classical), but it's not as impactful on other keys that merely have A in them. Resonation carries harmonics from the harmonic series, and you will find that the first members of the harmonic series (besides the tonic and the octave, of course) are the fifth and the fourth, the next is the minor seventh and then the major second. So there's diminishing returns as you drift away from any scale with A that doesn't have D, E, and G. Though at this point, it's not as relevant.

The major thing really is that you tend to spend more time on A in an A scale. And the fact that it resonates so fully reinforces it as the tonic. It can be a little strange when your subdominant is more robust than your tonic.