If we are going to talk about the ignition system asa whole, the spark plug wires, as cab said, only have a simple purpose to serve. "a coat hanger" could do the job. What I have seen on lab scopes where a real loss in energy comes from is the rotor air gap, and the plug gap.

THE ROTOR AIR GAP "RAP" is the gap between the rotor and the distributor. It is a huge gap!!! it takes a lot of energy to jump that, then it travels down its insulated and isolated wire to do it once again. A really good wire, will have a nice boot on it, that can take some heat, some pulling, and just plain neglect and still not let any energy short to a ground.