Aging of instruments is like the aging of wine. Sometime it's an enhancement, sometimes it's a detriment, and sometimes it makes no difference.
A local winery I was visiting found a case of Riesling in the back of their warehouse that had been sitting there for 9 years. When the wine was first made it was rather poor and the winery sold all of it off cheap. But they missed this one case. When they later discovered it they were just going to dump it in the drain - it was a poor year for Riesling. But the executive wine maker stopped the dump and tried a taste. He discovered to his great surprise that the wine had aged beautifully and was quite exceptional. I bought most of that case and have to say it was amongst the best Rieslings I have ever had. And I've had a lot.
I have handled many "vintage" instruments in the course of my work. Some are old, beat up and really poor. Some are immaculate and still poor instruments. But a few have shone, beat up or otherwise, and I am not convinced they started out as being superior instruments. Some of us get better with age, some just break down. I like to think of myself as the former.
Regardless, wood goes through changes as it ages. So do the magnets in the pickups. Whether those changes are for the better or not is unpredictable. And the quality of change can be a matter of taste. And buying a "vintage" instrument may be just as much about it's rarity in the market, or it's connection to history, or any number of other factors, as it is about the quality of the instrument.
