Since the plug gap is basically infinite resistance any resistance offered by the spark plug is irrelevant.
Yes - until the arc is struck then the resistance across the plug gap falls dramatically to the point where excessive resistance in the plug circuit will have some effect as some energy will be dissipated in the resistor reducing the energy that would otherwise be dissipated in the spark. It can't be otherwise. It's simple ohms law. Well maybe it's not simple but it's still a fact.
The link I posted demonstrates that if you go on adding resistance the spark eventually gets weak enough not to fire a plug in less than perfect conditions.
Now the real question is whether this reduction in spark energy has any practical effect on engine running. For most people there may be no practical consequences as a good electronic ignition system has so much excess energy available that it can afford to lose a small amount across the resistor.
A points ignition system may not be able to always afford the reduction in spark energy in all circumstances because it only has half as much as the electronic ignition to start with (or more probably less than half because of less efficient switching).
BMW designed the points ignition to have 1000 ohms in the plug circuit. 1000 ohm plug caps are very hard if not impossible to find these days so many people are having to run with a 5000 ohms plug cap and this doesn't seem to cause a problem. Adding another 10,000 ohms with a resistor plug is just asking for trouble though.
I need a lot of convincing that 15 times more resistance than BMW intended is not in some marginal circumstances going to provide me with a weaker spark than the engine requires.
And "The amount of resistance is inconsequential" is too much of a generalisation to convince me even if it did originally come from a BMW source.
