The other common plating metal is nickel. To answer you question: No, there is no sonic difference b/w gold and nickel plated jack beside feeling good  . In fact, gold isn't a very good metal for conducting electricity. We use it cause it has very good resistance to corrosion.

No, silver is the best, and copper isn't bad either. Gold is n't too bad but not as good as the other two. The problem is of course silver and copper oxidize very easily, so we use gold instead. Nickel is actual much worst than gold in conducting electricity, but for the purpose of plating (which is very very thin layer), the difference is negligible.