I think there is a substantial amount of magical thinking that leads people to specifically value gold or silver, and advance justifications for those metals as currency standards after they've already made up their minds. If they were starting from their claimed justifications, and simply looking for durable, rare substances whose production is limited and cannot be rapidly increased, then I'd expect as many cries for the Selenium Standard as the Silver Standard.
That hits the nail on the head. They're bandwagon metals, which is why they have a history of multi-hundred percent price spikes.
I find it highly ironic that the crowd which blasts the dollar for being valued far in excess of its intrinsic worth is the same crowd that champions gold and silver, two metals (especially gold) that are valued grossly in excess of their intrinsic worth. The industrial demand for gold take alone would place its price at only a fraction of a fraction of where it currently is, and the same goes for silver (which is why it's historically traded around the $5 mark, except when bandwagons form).