Try replacing the coil wire. The distributor cap does look odd. It almost as if the ignition is jumping accross a air gap before it reaches the distributor cap. This will cause the ignition to fire hotter than usual. A old trick to get a oil fouled plug to fire is to make the ignition jump a air gap before reaching the plug. I suppose the same thing can happen if the coil wire is breaking down. It would account for both symptoms.
steve