Maybe it’s applied in such a thin coat it’s conductivity isn’t so much an issue.
That is my understanding, but then why does it sound the way it does? How can a few microns of a coating make a difference to the sound? No idea, but it does. Cardas and all those other plug, connector and cable companies must have had some reason to use it over brass/silver/gold. Caelin Gabriel is the only guy who has stated he didn’t like rhodium to my knowledge, and does not use it in his stuff.
...on the all copper is your attaching bare copper wires to it anyway some decades old
You know, I’ve never thought of that. It never occurred to me to clean the ends of the wire with some emery cloth. Obviously I don’t think the most anal and eccentric audiophile would do this on a regular basis, but yeah, if you’re installing the plug it would be a good idea- why not? I am sure some audiophiles use some deoxit there.
And silver tarnishes too, don't forget.