[VT_Drew]

>e) No other use - Gold is terrible for most other things

Not true, Gold is one of the best conductors of electricity and is used in electronics and wiring.

[Symmetry]

Right. Gold has lots of practical uses and if it was valued according to them it would be worth at least as much as Bismuth at $25 per kg. But of course gold is $40,000 per kg.

[svs]

Yes, but not at the time gold rose to prominence as a currency. In those days people needed mostly swords and axes.

[DanBC]

Gold's not a great conductor. It's used because unlike copper or silver it doesn't tarnish.

And because it's shiny so it looks good in adverts.

[vox_mollis]

This. Also, you can durably plate other metals with gold only tens-to-hundreds of atoms thick, so actual mass usage is kept very very small for these applications.