Solid core wires allow for a pretty heavy current flow in the secondary ignition circuit and usually result in rapid deterioration of the distributor rotor tip and the distributor cap terminals. There's also a pretty strong magnetic field inducded around the plug wires that used to play havoc with AM radios and VHF TV signals. FM and UHF receivers don't have as much of a problem with the induced noise.
The increased secondary voltage available with electronic ignition systems has the potential to do more damage from solid core wires, but only if there's a wide plug gap or other reason to let the voltage peak out like a plug wire falling off, etc. Clean, properly-gapped plugs will keep the firing voltage down below 10K volts, regardless of what the open-circuit capability of an ignition system is. The coil simply cannot develop more voltage than is necessary to jump the plug gaps.
Jerry
