Coming back to the original subject, I was sitting on the throne last night pondering this issue, and it occurred to me that a few things might be as, if not more, important than the conductors themselves:
#1 The connection between wire and termination: no matter how "good" the wire proper, if it's not terminated in the RCA plug properly, any benefit of a "superior" conductor is going to be overwhelmed. I think this is probably as, if not more, important than the quality of the cable itself, as any change in conductivity at a joint will have a very pronounced effect.
#2 Shielding and cross-talk: cross talk is a real phenomenon, even on short cable runs, so routing you interconnects away from power cables, speaker cables and even other interconnects will be beneficial. Good shielding will help reduce cross-talk.
#3 Clean connections are better connections: you should ensure your RCA connections are thoroughly cleaned, then degreased once in a while. Try and program it in like changing your smoke detector battery - every time the clocks change or every six months or so. I also think the very act of changing one old dirty interconnect, disturbing the gunk on your component CD player, amp, whatever terminals, and bright shiny RCA plugs (hopefully) on your new interconnect may be why a new interconnect might sound "better" than the old one.
After that it all gets a bit high tech and electrical engineering to the nth degree. In my business, we use subsea cables or umbilicals to control oil wells etc. on the seabed, often up to 20 miles or more long, and the umbilical engineers get very picky about the electrical characteristics of the conductors, in terms of impedance (resistance, inductance and capacitance), frequency response and attenuation across the frequency spectrum, etc. etc. ad tedium.