RCA cable design

The "signal" is the voltage level versus time between the center conductor and the ground potential at the destination.  In an ideal cable this potential (voltage) is the same at the source and destination.

In an ideal termination, any current flowing in the center conductor will be in perfect phase with the voltage.

In "real" cables there are slight out of phase current flows due to capacitance, induction and dissapative dielectric losses in the non-conducting materials.  This will cause slight variation between the voltage at source and destination.  In other words,  cables will have a transfer function.

Cable designers should strive to make the cable have a transfer function which is equal to 1 (ideal cable).   However a non-ideal cable can have transfer functions that make it sound pleasing.  These like other elements in our systems are really distortions.  But not all distortions sound bad/

Tough crowd. Signal doesn’t flow. Current flows.
The signal is a time varying electric field between the two conductors. It exists at the input of the cable (source) and everywhere along that pair or conductors.

Where is the signal (electric field)? Simple answer, it is everywhere.
Now that electric field will tend to induce some currents (that do no work) in the cable.  That is where the mischief or magic happens. Some mischief can sound good, but its still mischief.

All that matters is that V(t) at the termination is equal to the V(t) at the source.  The ground conductor as well as the insulation properties between the source and destination plays a role in this.

To achieve an ideal transfer function =1 you need to minimize the reactive currents in the cable.  The ground conductor plays a role in this.

You can have a lousy quality center conductor and an equally lousy ground conductor and the effects can cancel each other out to provide an ideal output at the destination side.  Buts its a lot harder to do it that way.

" So if you have one conductor made of, say, copper, and the other of, say, silver, and the two conductors are of significantly different lengths (one is straight, the other is spiraled around it), what effect would that have? "

It would have the effect to make the gullible transfer more of their net worth to an audio equipment manufacturer.

Anyone should realize that before the RCA connector on your device the signal path and the ground path have totally different materials, shapes and topographies right? The same after the termination.