Ignition Systems and Spark Plugs
In my many years of working on Vehicles I have found that there is no magic in Spark plugs. With Plugs that have multiple electrodes all those extra electrodes end up shrouding the spark and in my opinion do the exact opposite of the claims they make. The best plug for power or mileage would be a side or surface gap plug because the spark is almost completely unshrouded from any electrode. I am sure the power difference is minimal if any but some modified cars require a side gaped and indexed plug because of possible interference with the Dome on High compression pistons. I have used about every Spark plug known to man. At one time I owned an old Toyota pickup that I was trying to increase the power and mileage on and can tell you that none of them made a difference.
On to material. Are expensive Platinum or Iridium plugs worth the money? Well, Copper is more conductive the either of those materials so it should produce a better spark. Now if the plugs are hard to change like a 5+ hour job then it might be worth it but the copper plugs in my Wifes car have over 40,000 miles on them and the electrodes still look good so that one is very debatable even if a plug change is a big job. How to tell if a spark plug is still in good shape. What wears on plugs is the electrodes, as long as the edges on the electrodes are not rounded and the plug is still firing then they are good.
To finish I will talk about special ignition systems like MSD or other aftermarket boxes. MSD means Multiple spark Discharge and honestly it only produces multiple sparks up to 3000 RPM where it is needed the least but the reality of it is that multiple sparks would not work at all at higher RPM, Just not enough time to create more than one spark . In my opinion Multiple sparks are kind of a waste because once you have ignition the air fuel mixture will burn. I do not believe multiple sparks will create a complete complete burn but these boxes do create a much hotter spark and that is good for ignition but could cause an increase in wear on parts like the cap, rotor and plugs, probably not what you want on your daily driver. As long as you keep your factory ignition system in good working order it will give you many years of dependable service, the only time you will need something better is if you have very high compression, Nitrous or large amounts of boost. BTW, I run a standard GM HEI in my race car. There are good aftermarket modules and coils available that will allow it to operate over 7000 RPM without a problem but the physical size of the unit can cause interference in some applications. I have run an MSD and it did make the car sound different and I had to change the timing curve so chances are I could be wrong about this but it did not do a thing about mileage.
Spark plug Wires? Most computer controlled vehicles will need to resist ignition wires. Again there is no magic but look for something that is durable. I have found that the OEM wires are the most durable but can be somewhat expensive. As long as your car is not computer controlled you can run solid wires but be prepared for the possibility of interference with your radio.
So that is my opinion on ignition system. In theory, for the best performance and economy, use standard (Copper) plugs that are side gapped and an aftermarket ignition box but chances are that you will not feel or see a difference in mileage or performance unless you have a heavily modified vehicle or your factory parts are in bad shape. Bottom line, keep your factory ignition parts in good shape and they will give you everything that you can hope for.