I have a buddy who collects all things Glock. He has most if not all the models and variations within the models - no G18, though. He even manged to find both a G25 and a G28. With the exceptions of the G25, and G28, I believe most, if not all are NIB. He has the knives, tools and all sorts of promo stuff. To me, it is a pretty impressive collection!
I collected a bunch of military surplus firearms pre-2008. They were cheap and under $200. I collected them because I like(d) them. Now, I look at them as an investment.
Mosins (Russian) were $50, on sale 15-20 years ago. They were a dime a dozen. Even up until a few years ago, they could be had for ~$150. Now they seem to start at $400 and are going up. I think the most I paid for any milsurp was $350. Almost every single one of the milsurps I have is over $300, at least, looking at GB prices and stuff being sold on various websites.. Right now, I'm just sitting on them. I'll sell them, eventually...