Why Rhodium?

Rhodium is not only a poor conductor but IMHO too hard.

To get a good grip on an outlet or speaker or any other contact you want a soft metal.  Something that will deform under pressure, allowing for serious grip, especially for AC plugs, sockets and spade connections on speakers.  Pure copper or gold plated copper will absolutely outperform Rhodium for reliability alone here.

Rhodium, as pretty as it is, is really a terrible choice in this manner. 

It's shiny, but most of the time I find it too hard and slick to offer good grips.

I like my contact metals soft and springy. Hard spades for instance are nearly impossible to tighten well long term. Gold over copper however has enough malleability that the speaker terminals bite into them when tightened.

In power connectors they seem to make it a lot easier for plugs to slide in or out.

I love how they look.  Like jewelry, but never had a good experience with them on a practical sense.