Metals are a good way to short the dollar. They move inverse of the dollar due to exchange rates. They also have a fear factor that comes into play when stocks drop. They hold their value compared to other items like oil, coffee, sugar, and others. An oz of gold buys about 13 barrels of oil. If you like do a chart of the amount of oil an oz of gold buys.
Mining stocks just leverage yourself to the price of the metal.
This isn't about the metals IMO. More than silver and gold have gone up substantially in the past few years. It's about commodities in general, due in part to years of supply/demand imbalances and, more currently, substitutes for buying the $. BRK may not be able to participate in commodities to a significant degree because of the amount of movement many billions into any one commodity would have on the price - both buying and selling. Foreign currencies, however, are another story in that regard.