Usually I only value old instruments when they have features that you can't find in new instruments.
For example take this "budget' Harmony acoustic, the 1260 model:
These were made in the late 50's, 60's and early 70's. They would be impossible to make today.
The neck is solid one piece Hondran mahogany.
The back and sides are solid Honduran mahogany. (by "solid" I mean the back is a single 16" wide slab of quartersawn wood unlike Martins and Gibsons.
The top and all bracing is solid split billet red spruce.
The fingerboard and bridge are Brazilian rosewood
The finish is shellac spirit varnish
The glue used is hide glue.
Built in America.
Adjustable truss rod (don't laugh, Martins didn't have one until the 1980's)
This was the acoustic that the baby boomer generation grew up on. It's acoustic guitar that Jimmy Page used to play the most famous acoustic guitar piece in the history of rock and roll: the intro to Stairway to Heaven. Lots of famous rock stars learned their first chords on a Harmony Sovereign on both sides of the Atlantic.
What a newly manufactured would one cost to buy today that is perfectly accurate? Probably over 2 grand retail I would imagine.
They sell all day long for around $500 on the internet. Less if they need work done.
My point is that THAT is the definition of a "VINTAGE" guitar. Something you seek out because they don't make them like they used to.
Some plywood Japanese guitar? Get out of here with that crap.