Unless a gun is ALREADY a collectible, having one that is NIB and keeping it that way in hopes of it's value appreciating, is a bit like playing the lottery. The odds of you actually coming out ahead are about as slim.
As I've noted in these discussions, before, the values of guns seldom keep up with inflation. For example, using an inflation calculator found on line, that uses the actual change in the value of the US Dollar over time, a gun that cost $600 in 2000 would cost $751.98 in 2010. Just getting your original investment back is hard with most guns.
{Here's a link to the site: try it with some of your guns. It's only good up to 2010; they update it from time to time.
http://www.westegg.com/inflation/infl.cgi)
For most of us, about the only way to make money on collectible guns is to find a gun that the seller doesn't know is collectible. Then, if you buy it for a low price, you're taking advantage of that person's ignorance. Not illegal, but maybe unethical.
Shoot the darned thing.