The problem is, once someone defines another as a "collector," everyone wants to sell that person something "rare."
A collector/accumulator/investor can be the same person, but doesn't have to be. I personally hate labels- I just buy, keep and use what I like, regardless of monetary gain- however I would like to break even eventually.
The worst problem is that many times emotions get involved if a person is passionate about his hobby, and that's when sellers to "collectors" make a great deal of money. There is absolutely nothing wrong with this, and it helps the hobby in many ways- such as attracting attention to the hobby, makes pieces go up in value and more history and facts may come to light increasing interest . On the contrary, it can make pieces go down when items become overvalued and inflated through dishonest conduct of rouges, ruffians and just plain greedy people...what happened a few years ago in the high end Winchester market is an example.
As for an investment- whether it's guns/coins/stamps/plate glass or anything else- they will only increase in value if someone is willing to buy it for a greater price- regardless of scarcity or condition. (Not to be confused with
intrinsic value and/or
value of use to a buyer)