If you are planning to keep for a decent length of time, nothing to worry about. My first "vintage" purchase was a '55 LP Junior in 2008, in "beat but sweet" original condition. I paid WAY too much for it at the time ($6000 US), and could have felt pretty sore about that after the markets crashed. It was probably worth $3500 on a good day in 2011 when people had the confidence to start buying and selling vintage guitars again. You can definitely lose in the short, even medium term.
But here's the thing. That guitar is a "magic wand", light, resonant peach of a Junior that will be among the last few I'd ever sell. When the market started moving again in 2011, rather than bemoaning my loss of value, I bought a couple more old Juniors in better condition. A '57 for $3500, and a '59 for $4500.
A lot has happened in between times, and I've found myself needing to thin the herd a bit just for the sake of space. (I think 38 of them, but I kept getting distracted by the guitars while trying to count them. I think 13 Les Pauls, but I get especially distracted by those.)
The $3500 '57 Junior ended up on the list of guitars I had to part with. It is currently on commission sale with a very good UK vintage dealer for £9,950 (that's about $13,000 US).
If you buy a guitar you love, and you keep it, I don't think you'll ever lose. Yes, the Boomers are dying off, but plenty of Gen X guitar heroes and fans left. Gen Y definitely don't have universally poor taste in music and instruments. Most importantly, there are more people being produced every day, but there is a limited pool of 50's Gibsons, and 60's Gibsons of specific interest.
My main worry now is how slowly I'll need to sell off guitars that I don't really have space for. In some cases I'll be making enough that I'll need to declare them for UK capital gains tax if selling more than 2 or 3 a year.