Wouldnt a capacitor work better? Plus you want the spark as hot as possible and a resistor would lower that. I have no idea what the ohms are if its like 10 ohm or 100k, I dont have one to test. I know putting a ceramic cap across your alternator will reduce noise but a resistor in the plug? Plus its going to get super hot and change value.
From my point of view:
Without the resistor, once the spark jumps, the wire capacitance would cause a very short but high current pulse, generating a lot of EMI due the oscillations at the cable resonance frequency (depending on its LC characteristics), this could cause the voltage to reach even higher levels than it originally had and cause damage the driver. Not to mention the noise taken by all nearby electronics.
That's where the resistor comes to help. It limits the peak current, greatly avoiding the oscillations, but lets the voltage rise as fast as it's generated, so the spark will work the same.
A capacitor would filter the spike, reducing the peak voltage, requiring longer pulses for the spark to jump.
Once it jumped, the current would be higher, worsening the EMI worse and shortening the life of the electrodes.
You can see it yourself very easily. Take a small capacitor (ex. 10uF 16v) and attach a 1m cable to it.
Connect the oscilloscope in 10x mode at the capacitor pins. Charge the cap.
And check the difference when directly shorting the wires or when doing so through 0.5ohm resistor.
See the difference when shorting out di