Guitars are lousy investments, financially. All the good investments have already been made. There are no "reasonable" old herringbone Martins anymore. Prices might still go up, but you have to start with somewhere over $5000 US, have it tied up for years, and the instruments have to be carefully and expensively maintained.

Some "reissue" models have themselves become vintage collectibles, notably the late-60's Martin D-45's. There were about 300 of these made and they now sell for about $25,000 US, representing as they do the end of the Brazilian Rosewood era.

It's guesswork, but if you find a guitar made by a recently-established luthier that seems particularly fine, that's at least a good buy, and if the maker turns out to be the next Grit Laskin or George Lowden, its value will soar. Probably won't happen but at least you have a good guitar at a good price--not the worst thing that can happen to you.

Frankly, I think buying a guitar NOT TO PLAY on the hopes of making a financial killing later, is shameful and immoral. Guitars are made to be played, and should be available to players who are willing to pay a reasonable price for them, not hoarded by would-be millionaires to make them even less attainable to players.

Willie-O