I think it also hinges on your outlook of the country and the world prospects.
If you think that America is going to keep going along at the same pace and most things on the horizon are positive, I would expect guns to stay flat. Meaning that as long as you make sensible gun purchases (buy quality used guns) then you'll break even, maybe make a small profit. Also, niche historical guns may command a premium if you can buy something, learn the history, and there is antique or unique quality. Same with ammo.
However, if you are pessimistic about the future and you see a lot of civil unrest, high volatility in the markets (stocks, oil, precious metals), then guns and ammo will be among the most valueable items. It doesn't take much for the .gov to turn off the NICS checks and for shelves of ammo to run dry. As we've seen in NOLA, the LA Riots, and around the world, civil unrest can occur nearly instantly and as fast now as the speed of communication. With the REAL problems the US faces (debt, oil, poverty, unemployment, 10+ year war, etc.) one could say that we are in for a long strecth of bad times. We've seen what happens to guns/ammo prices when there is some concerns - during Obamascare or after 911, prices went north overnight and supplies dried up. Imagine a shortage of anything that is in the supply line of guns/ammo. Oil, gunpowder, primers, copper, you name it... Buy it while you can if you are pessimistic about the future.
+1 to teaching others the skills to shoot.