This is an interesting question. I think it's very hard to predict. I got bit by the bug a decade or so ago and started collecting very nice rifles. I had NIB Browning B-78s from the 70's, a really nice Mark V from that era and several AAA Claro Walnut Coopers. I still have some of them but the market seemed to go soft on this kind of stuff with all the advances in stocks, bedding, lighter weight, etc. I tried to sell one of my AAA Claro Coopers last year and my dealer told me that people just aren't very interested in them the way they used to be. I'm currently in kind of a transition in my arsenal, leaning toward lighter weight rifles with more current stock components/configurations. I am definitely hanging on to some of my "wood" rifles in hopes they will "come back" and be popular again, at which point they will probably be inherited by my son (currently 13) as well.
So, your guess is as good as mine as to what will increase in value and be the "cat's meow" in 30 years.
I'll tell you one rifle I would like to have NIB to put away for a while would be a maple stock Browning A-bolt in .243. Just cuz.
Cheers!