I think the concept of "opening up" is a myth and just reflects the listener's hearing change and adjusting/getting used to the tone of the guitar.
Merlin don't get me wrong but we're on opposite sides of the fence on this, and this is more for Zeboma's ( or soembody else new to the topic)'s benefit
I do feel particularly qualified to offer an opinion because I have in fact owned 3 different Guilds since new and over the course of their lives 2 of them have in fact increased the time it takes for a note to decay to complete silence . ( I haven't measured the F65ce recently)
Since nobody ever seems to offer a
measurable definition of "opening up", I arbitrarily picked an acoustic characteristic that was very easy for me to measure and replicate: "decay time".
I'll skip the test methodology for now, but:
The D40 in particular was always the "sonic runt" of the litter and over the last couple of years its sustain (as
measured by the observation noted above, decay time) has in fact increased.
I'm absolutely certain volume has increased too but I never had an easy at-hand way to measure that.
I think the single most important factor affecting/"improving" tone is not so much simple age as accumulated playing time.
The D25 had a "big moment" at about 200 hours, that only took a little over a year, and actually I wouldn't have thought it could happen that way if I hadn't experienced it myself.
The D40 got a lot less playing time and only got into the 200 hour neighborhood about a year and a half ago, but it's now jalmost twelve years old as well.
I do recall somebody well-respected in the world of luthiery offering an observation that most guitars hit their prime at 10-15 years, but I can't recall exctly who it was, either Bob Taylor or somebody associated with Fender come to mind, but they were quoted here.
Fianlly, recently we had another discussion about the phenomenon and our member Christopher Cozad made some points a bit more elegantly than I could, see post #28 in this thread:
http://www.letstalkguild.com/ltg/showthread.php?185145-Acoustic-Guitar-Opening-Up/page2
In fact you participated in that one so you might recall it, but I'm linking it more for the benefit of Zeboma since as you mention yourself there really are a lot of things going on as a guitar ages, like how NCL continues to get lighter and more resonant as it ages..
To me the real question for Zeboma would be "Do you
want to own the guitar for a long time and "grow old" with it?"
It sounds like you're saying "No".
I bought mine "for keeps" but I could never replicate the playng time they have now, so I get when folks want to look for an aged tone and not wait for it.