This seems like a bad idea. Firstly, the melt value of a nickel is less than $0.05 [1]. Maybe he was confused by the fact that it costs more than $0.05 to mint each coin; that's because there are costs other than the materials. That also means it'd be cheaper to just buy the metals that are in the nickels than to buy the nickels if you wanted to bet on their price. If the government switches to a different composition, there will be less demand for nickel and copper, which doesn't bode well for the melt value increasing significantly beyond $0.05 because of a switch.

Secondly, just holding the nickels doesn't mean you're sure to not lose any money. As you said, simply stuffing cash (or nickels) under your mattress means you're losing some every day to inflation. You're also losing all the potential gains of the other things you could be doing with that money other than piling up nickels. At the very least, you take no risk of losing the principal by sticking it in a savings account (~1% APY) or buying a 1-5 year CD (2-3%).

Then again, I don't have a couple million dollars to blow on stockpiling nickels. The sage investor must know something I don't.

1: http://www.coinflation.com/coins/1946-2007-Jefferson-Nickel-...