As a long term investment, I'd look elsewhere. Short-term, you are likely right.
Vintage guitar collectors and buyers are pretty much confined to a certain demographic (the baby boom generation.) As that generation ages, they or their children will sell and not buy.
I love vintage guitars, but nobody my age cares about Duane Allman or Billy Gibbons.
I'm just wondering how old you are? With your interest in vintage Fenders etc I assumed you were "mature"? 
I can fully accept that most young people aren't particularly interested in Duane Allman or Billy Gibbons - 1973 is ancient history to an 18-year-old. I'm aware of The Tornados and Johnny Burnette and the Rock and Roll Trio, but I can't say I feel much connection with them. And looking in the other direction, I don't know the bands young'uns listen to so why should they know the bands I listen to? Great if they do, but times change.
But isn't that statement about vintage guitar collectors/enthusiasts a bit contradictory? If they're "pretty much confined" to the baby boom generation, you must be the exception that proves the rule. And who are they going to sell to if the collectors are rapidly dying out?
I am 38. In 2009, 38 is not a kid, but not the boomer generation either.
But the fact that my love of vintage Fenders makes people assume I am older sort of proves the point.
Anyway, to whom will the vintage collectors sell to when their current market is out of the market? Probably they will sell to anyone who is willing to buy, at whatever price the market will support. Just like the crack about TwinFan buying a Pearly for UKP 7000 in 30 years: why, when he will be able to get one much cheaper (at least in inflation-adjusted terms.)
In the US, before the Beatles hit,
accordion was a very popular instrument. After the British Invasion, you could not give an accordion away at gunpoint to a teenager. The decline probably will not be that catastrophic.
