I think you should also ask yourself: What are their uses? And are they still valid in a post-singularity society? Platinum is useful in fuel cells as a catalyst to improve their efficiency. It is also useful in making optical fibers, and thermocouples beyond its uses in jewelry. Silver is resistant to corrosion and oxidation. It also is a good thermal and electrical conductor. Its photo-sensitivity has given it a place in film photography. But it is also useful in key electronics thanks to its thermal and electrical conductivity. And once again is used in jewelry.
The use of gold goes beyond mere jewelry. It is also beaten into thin sheets as gold leaf to be placed on all manner of things. But beyond its cosmetic appearance it is quite useful elsewhere. It is useful in the protection of electrical copper components because it does not oxidize which could break the contacts. It is also used in computer chips for the production of circuits.
Copper is common, more so than gold, silver and platinum. It is useful as wiring and in motors. It conducts heat and electricity very well making it useful in computer electronics and industrial settings. My first two questions are also answers with everything else as descriptors for the metals. They have their uses in current 21st century devices and the like. But are they still as useful ICly? I believe that is a good driving point to base value off of. These are just some of the basic, but varied uses in our societies today. However their usefulness in SARP may or may not be the same, especially if alternatives can be had and produced cheaper or in greater quantities.