My opinion is worth very little without adding in my own inflated sense of self-importance.
...For the OP, I think most people believe the sound of a guitar will change over time, in the first few years after production, but the explanations are varied and generally unprovable.
Regarding acoustic guitars "opening up" over time, there is little scientific data for or against, as establishing an observable process having credible management over 5 or more decades has been relatively impossible to achieve.
However, much anecdotal "proof" exists (veer: for those experiencing something personally, something that you are unable to repeat, I propose this in no way diminishes the truth of the experience), the most significant coming from, perhaps, an unexpected source.
Most builders agree that there is a quantifiable change in an acoustic, stringed instrument from the moment of it's inception to a period ranging from a day to a week after strings are applied. Much of this change can be attributed to things "settling in", a rather easy-to-comprehend concept for a builder (For those who can extrapolate, I invite you to extrapolate).
This incontrovertible change leads us to
hypothesize that change will continue.
This change will slow, but there will be a noticeable difference in the sound of the instrument several months later. To identify the change, the guitar is played and compared to
memories of the sound of the guitar at it's birth. Before entirely dismissing this latter experience, I would suggest allowing credence on the basis of the credibility of the collective of builders. It is safe to say that all guitar makers who participate in some form of a "voicing" process of their instruments will build a veritable database of sounds in their memories (Poo-poo it from the outside if you will, we will chuckle knowingly from the inside ;~}).
This comparative memory is expanded over time to accommodate the distinctions that occur when selecting wood, determining size and shape, bracing patterns, etc. What it sounds like before is not what it will sound like afterward, but there is an identifiable relationship, and the better one gets at connecting the dots, so to speak, the better one can be at predicting the outcome. The process, while beginning much like the solo card game of Concentration, becomes second nature over time.
I say this to emphasize the point that hearing is believing.
I realize that not everyone has the opportunity to experience this (anecdotally) and this is precisely what prompts me to share the information. Do changes result solely as a result of the forces of string tension against wood, bending, bowing and pulling? Are tonal changes attributable to the inevitable changes occurring in the wood lignin and cellulose? Surely, as the hemicellulose of the woods evaporates and the organic compounds dry, harden and crystallize, this is affecting tone. Is there a truth to the hypothesis that alterations are occurring to the wood fibers at node points, much akin to the realities of stress fractures in infrastructures? Is it torrefaction or torrefiction?
But buying a guitar now in hopes that will sound better later seems to be a bad strategy.
Would it be fair if I stated that "Buying a guitar that sounded quite impressive today, with the expectation that it would, one day, open up to sound even more impressive is totally acceptable"?
Might it also be fair if I reinforced that "Buying a guitar that sounded unimpressive today, in the hopes that would, one day, open up to sound impressive" is likely a fools errand?
