balast would have an effect on spark plug voltage, usually the plugs will stt 30kV, without the balast it might go up to as much as 35kV, but electroplating? Assuming it could the balast would not effect that much, the balast lowers the voltage to the coil from 14 or so (which is what your alternator should be putting out) to 12. Take the regulator out completely and I bet you'd have 19V, There are contacts in the regulator which are obviously no longer working.
As you said, your car would NOT stall unexpectedly, you said it would stall when it heated up for a while, sounds like the ignitor to me, but by adding the balast back, it might not get as hot and probably is marginal now.