This is a fascinating topic, and one that's interested me, as it seems both intuitive and highly subjective, that any wooden instrument's tone could be affected by age, and by how instruments that were played frequently could exhibit better tone than ones played infrequently, or not at all.
Toby Faber's book "Stradivari's Genius" was the first reading I ever did on the topic of vintage stringed instruments, from the standpoint of how one man or group of men could set a standard for construction of instruments that survives to the present day, 250 years after the end of the Cremonese Golden Age of violin and viola luthiery.
I was led to this by the father of one of my students, who is one of the world's best-known dealers in vintage Strads, Amatis, Guarneris, and copies from both modern times and the so-called "golden age" of Stradivarius replicas, the mid-to-late 19th century. He stopped in on his way to demonstrate three Cremonese violins to potential local customers, both collectors and amateur players, and one symphony player. We discussed my construction of the Jazz-Bo (which was then being prepped for finishing), and then he opened a smallish rectangular case of odd proportion that he was carrying. It held two Stradivari and one Amati.
He handed me a Strad (I did not know just then what it was--it just looked old), and I took it in hand gently (I thought), holding it as one would hold a dinner plate; thumb on top of the body near the tailpiece, fingers splayed out across the back. He smiled and explained that one must not hold an 18th century violin in this manner; the heat of one's fingers would soften the varnish and leave fingerprints; one should grip the neck instead! The neck was roughly a third the cross-section of a Rickenbacker mandolin; with its curly grain it looks like it would snap, but it is quite sturdy, and what's more, the body feels virtually weightless. Too, the neck of any 18th century violin will have had the varnish worn away a long time since.
We talked about this, and he then informed me as I completed my inspection an handed it back to him, that this was a Stradivarius instrument. Gulp.
The Faber book says a good deal about varnish, but not a lot about the wood used, at least from the perspective of aging. It does hint, though, at mechanical and climatic fatigue being responsible for the decrease in tone and playability of many Cremonese instruments. Sort of like the metal fatigue that has spelled failure to airframes in aircraft. I saw this as a clue that, not only finish was involved in the process of an instrument acquiring its tone, but also the wood itself. Beyond selection of species and cut, there is the process of working the wood which can affect, not only the instrument's ability to "come of age", but also the disability of aging: an instrument built too feebly or out of balance will age too rapidly, and its own "golden years" will be abbreviated.
Eventually my reading led me to this paper:
http://www.phys.unsw.edu.au/~jw/reprints/IntaViolin.pdf
This is an abstract of a three-year study done in Australia, of the effects of aging and playing upon two specially-constructed twin violins. One, the control, was kept upon completion in a museum-type environment of highly-regulated temperature and humiditry; the other was played frequently and by many players over the three-year period.
Blind listening tests were performed. The conclusion? Counter-intuitive: there was no discernable difference in what the audiences heard from the twin instruments.
Wait a minute--three years? That's nothing, I thought. Studies have shown measurable differences in the dampening effects of the wood itself upon the music played on an instrument, due to excitation of the cellular structure of the wood fiber itself. Moreover, these effects are both good and bad--initially, they help the wood to "bloom" and sweeten the sound as it simultaneously aids in volume and projection (sometimes unpredictably, it must be admitted). Later on in an instrument's playing life, the wood can almost sound fatigued; seems entirely reasonable.
Longer-term studying of this phenomenon and related issues are surely in order.
Effects of finish are another topic entirely. Suffice to say that as more and more finish is piled on, the potential for tone change--primarily and most demonstrably in thin-walled, hollow-bodied instruments--becomes more dramatic. The natural response of the wood can be sharpened and deadened, and there is a fine balance that must be maintained.
When I complete an acoustic Rickenbacker, I string it and play it, then leave it strung for a period of time ranging from a few days through a few months until it's ready to begin the finishing process. The first coats of sealer make some difference in tone. I'd describe it as "focusing" the tone and crispening it. Laying on repeated coats of urethane clear, yields a guitar that sounds quite dead until the finish is mechanically flatted and thinned by about 2/3. Shrinkage pulls the coating further down onto the wood and into the pores, at least on the front. By the time the guitar is shipped, it's beginning to develop a tonal character, but is not yet in balance; there are bass and lower midrange frequencies and harmonics to be developed; this happens as the wood "loosens" up with frequent playing.
I might add that this is empirical, not theoretical; strictly from my own observations. If anyone out there can give me a bibliographical reference on this, I'd be most grateful.
That's a short answer. It would make a fascinating book for those of us who are obsessed with sound and music, and the craft and technology that creates both.
and I'm simply not able to cope with any finish issues other than the recommended ScratchX/Zymol-treatment 
You don't drive a manual transmission car, do you? 