Lately, I keep all my change. Theory is that at some point, the dollar will be devalued, maybe 10 to 1 ala Zimbabwe. It would be impractical to replace all the coins immediately, so they should appreciate in value in direct proportion to the devaluation.
And if it never happens, they still spend.
No they won't.
The only coins widely circulated that will appreciate are the copper penny (about 10%, in circulation still) and the US nickel that this article is about.