US five cent coins contain over 7 cents worth of raw material as of this afternoon, mostly copper and of course, nickel. If there is inflation, the prices of metal will increase, and the coin will have 8, 9, 10 cents worth of metal. Pre-1965 dimes contain over $2.42 of metal today, while pre-1965 quarters have over $6 worth of metal. (www.coinflation.com)
If there is deflation, the coins are still currency at face value. They will always be nickels.
Hoarding nickels seems like a good investment for people without a lot of cash and with plenty of time on their hands. Each time you go to the bank, get about $20 worth of nickels. Store them in your house somewhere. There is zero downside risk. If everything is fine and metal prices fall, you can just spend them. If raw materials prices go up, as many people predict, you will win.
The reason this is not more popular is because of transactions costs. You have to lug around the coins. And you could not really get seven cents by selling them for scrap; the costs of separating and extracting the metal would be too high. But history tells us that coin collections tend to keep their value pretty well.
One word of warning: I do not recommend buying silver or gold coins now. I actually recommend selling gold or silver if you have any. And yes, prices have gone up since I said that, but I still think it is a bubble. Prices could easily collapse. But with nickels you do not have that problem.