The way the coil develops more firing voltage capacity is by building a better magnetic field around the windings. This is done by flowing more primary coil current than a set of points can handle. Without getting deep into the physics and electronics of induction coil operation, the more primary current there is, the hotter the spark will be. Points can handle around 5 amps without overheating and burning. A HEI coil carries around 15 amps, sometimes more as the current first begins to flow. It does this by using heavy duty power transistors instead of points.
The primary wiring from the battery, through the ignition switch, to the coil has to be capable of flowing the increased primary current, so yes, the entire circuit needs to be upgraded, not just the wire from the switch to the coil. The circuit from the positive battery cable to the ignition is usually pretty heavy to begin with, because it carries the current for accessories like electric wipers and the heater blower as well as the ignition, in most cases. It doesn't hurt to run a new, heavy wire with very good terminals there, however.
Jerry
