The following table gives an idea of the factors affecting the value of an investment in commodities (metals, food, and textiles)
The demand of the commodities remains the wild-card that can affect the rise and fall of the investment. For example there is a Super-cycle of production predicted from 2014-2020 to be driven by emerging -markets. This scenario could lead to a bull-run in commodities. However on the other hand global imbalances could lead to a stalemate where west and east refuse to consume leading to deflation. This could lead to a serious bear-run in commodities.
However the most revered store of value is Gold. The fact that it is not used in production insulates it to some extent from the demand-supply cycle. Most of the worlds Gold are in bullion.In fact the annual supply of gold is a very small fraction of the available bullion.Hence increases in supply cannot really drive down prices. The increased risk of sovereign default is sliding investors from the US treasury market to the gold market (Eg: RBI buying 200 tonnes of gold from IMF).
The market for gold is a very small percentage of the total investment in “safe assets” like US treasuries. Even a small percentage shift from T-bonds to Gold can lead to huge jumps in the value of gold. Considering this outlook..I think it is advisable to place ~ 3% of your investments in gold.