Ok, it's always good to check up on what's changed in connectors.
First, most RCA connector manufacturers publish NO data on their connectors other than mechanical specs. Switchcraft says nothing about contacts at all, same for Rean/Neutrik. Kycon publishes a little data.
The second thing to know is that the design of the inner contact on an RCA jack has changed somewhat, moving away from the full-sleeve design and toward smaller contacts. This would be a good thing, as larger contact surfaces reduce pressure, and increase the chance for oxidation. The new jack designs seem to have smaller dual-ridge contacts for the inner contact, and the same large cylindrical outer contact.
So, given the limited data published by one manufacturer (Kycon), I find that contact resistance is stated as 30 milliohms for their average RCA jack. Their contact material is tin-plated brass.
For 3.5mm stereo jacks, again very little data is published, again, nothing much from Switchcraft or Neutrik, but Kycon publishes a bit. Their average jack has stated contact resistance at 50 milliohms max, and contact materials are copper or copper alloy base with tin or silver over nickel plating. None of that makes any difference to the contact resistance.
Both jacks are life tested for 5000 insertion/withdrawal cycles.
So, what I said was incorrect, and you guys are right, RCA jacks have, on average, 20 milliohms less contact resistance. And, though I know I've seen them, I can't find any data on gold plated contact jacks of either kind.
20 milliohms is 20 thousandths of an ohm. In the grand scheme, the difference between 30 milliohms and 50 milliohms is negligible. It should be noted that those resistance figures are tested before a 5000 cycle life test. Post-life test figures are not consistently published, but are typically higher by 2X.
It appears that not all RCA jacks have higher contact areas than 3.5mm jacks. The contact material in both jacks is not usually gold, as with small contact surfaces, a soft gold plating would wear off quickly, so manufacturers opt for a harder plating material, and depend on repeated insertions for a sort of cleaning action.
My apologies, all, for the misinformation. My RCA jack data was outdated.