Is gold overvalued or undervalued? The following charts attempt to provide some perspective. Versus other commodities where you can see other commodities priced in terms of units per ounce of gold, gold appears to be fairly priced right now, except perhaps for food, where gold seems to be relatively expensive (gold buys a lot of food index relative to history).
Versus the equity market, either gold appears to be cheap or equities appear to be expensive. There was a super spikes of gold amidst a bear market in equities back in 1980, and we're nowhere close to that now. We could clearly say "gold is in a bubble" if we could buy 0.6 units of DJIA for one ounce of gold. Either that, or DJIA would have crashed and at that point be extremely cheap.
As a percentage backing various monetary metrics, gold seems undervalued in terms of the number of dollars divided by the total value of the amount of gold owned by the US Treasury. Either the Treasury needs to get a lot more gold, gold needs to become a lot more expensive, or the money supply needs to shrink if we are to back our currency using gold.
Conclusion? Versus paper claims on wealth (equity & money supply) gold is undervalued. Versus other commodities, gold is fairly valued in terms of historical price range.