Gold as a medium of exchange is no difference from baseball cards, postage stamps, etc.
A world of difference. Gold cannot be destroyed and won't change even after a million years. Go buried a 1 kg gold ingot and a million years later someone dig it up.... U still get the same shining ingot of gold; I can't say the same for your baseball cards and postage stamps.
Can I buy previously-issued BNM-issued gold coins from goldsmith shops ? Say someone needs cash and sell his gold coins to goldsmith shops so they can resell to others.