With a weak single coil electrical system a Platinum or Iridium plug will provide a stronger and more consistant spark.
However if you have a high voltage system with individual coils a copper plug will actually produce the stronger spark. It just takes a lot of juice to get a nice big fat juicy spark out of a copper plug.
The individual coil packs in our bugs provide a ton of juice and make a much better spark with Copper plugs.. the down side is you will need to replace them often vs a weaker but much longer lasting platinum plug.
No offense but this information has some holes in it, the Iridium plugs are made of an extremely hard and strong metal with a higher melting point and this allows for a much more durable and effective spark with an electrode that is only 0.4mm in diameter. The design factors that have gone into the Denso Iridium actually decrease energy consumption and increase spark intensity and focus thereby making A/F mixtures smoother and more consistant.
The production of a stronger spark is good but not if the spark plug produces it inconsistantly, with greater energy consumption and without focused intensity like in the case of the typical standard or copper plug.
The ignition system voltage really wasn't an issue even back when domestic muscle cars had a strong presence on the streets with the use of powerful ignition modules and coils from companies like MSD, Accel, Jacobs etc., it certainly isn't a problem with most of todays vehicles which come from the factory equipped with stronger more technologically advanced electrical and ignition systems.
This having been said, for the combination of superior performance, spark intensity, spark focus, spark consistancy and spark plug longevity, you can't beat the Denso Iridium, especially in import high performance and forced induction engines.
Manufacturers are encouraged thru competition and the EPA to make tuneups as infrequent as possible so platinum and iridium plugs are very very popular.
The real reasoning behind manufacturers introducing more and more cars that are made to appear to be lower maintenance is very simple, most people just want to get in a car and drive, they don't want to deal with maintenance issues or anything else for that matter, it's a turn off and a large component in making their choice of which car to purchase.
Bottom line is, the appearance of a lower maintenance vehicle sells cars and this is a car manufacturers primary reason for existing $$$$.
I happen to like that longevity and am not having any detonation or pinging so I'm sticking with the exspensive plugs on my buggy but if I was having issues... I would actually got with the el cheapo copper plug.
