Bro i think you misunderstood, and the link you mentioned is talking about iridium spark plugs. Which material is used in spark plugs is another debate.
I was talking about the resistance which is deliberately placed in the centre electrode of the spark plug. For example for toyota K16R, "R" here denotes that it is resistor type plug. Which means that in the center electrode, there would be resistance and purpose of that resistance is to suppress Radio Frequency Noise generated by spark plug operation.
Resistors are essential but you need to look at the other parameters also, for example ignition coil in modern automobile provides up to 50,000 volts or even more for sparking. Now when you have this much high voltage, the smaller internal resistance e.g 5k ohm is not going to make difference in spark.
On the other hand, if you take an old spark plug, which has deposits on its centre tip, now those deposits can play a role in performance because the resistance introduced by those deposits would be much much higher.
