Spark plugs. Why is it so hard?

RRR,
You might want to try reading your own links before you criticise others. Your Champion link in post 17 says this about Plat, Irid plugs: ' decreases the misfire rate' & ' increases firing efficiency'.
NGK link, post #18 about resistance. Do you know what the 'n' before the ohms symbol means? It means 'billionth'. So the copper resistance was 16.78 n-ohms or....drum roll....0.000001678 ohms. And 0.00000693 ohms for nickel.
The copper was NEVER used in spark plug cores to reduce electrical resistance because it would have made no measurable difference to the spark current because of all the other resistances in the spark cct [ the resistor in the spark plug alone is between 3000-6000 ohms ]. The copper was used because it conducts heat better. Nothing to with with it's electrical properties. It heated up the tip quicker to burn off deposits, stop fouling.
Some people have learned nothing from automotive history, when the plugs were 18mm big, used magnetos for ign with 0.015" plug gaps. Bigger gaps don't help? Hmm, why aren't we still at 0.015"? Somebody forgot to tell Honda because they built an engine decades back that had a miniature combustion chamber next to the main chamber; idea was the small chamber to be ignited by a spark or glow plug & the small chamber bonfire ignited the main chamber.
Plug gaps have got bigger [ not smaller, funny that ? ] over the years as innovation has provided improvements. Phil Jacobs, founder of Jacob Ign Systems claims the ideal plug gap is 0.100"; mentioned more than once in his book, Performance Ign Systems. Hmm....MSD recommends up to 0.060" gaps with the 6A box & up to 10.5 CR. Hmm. Accel 300 unit, 0.040: plug gaps for 12:1 & 0.050" or more for lower comp ratios. Hmm. DUI, Chrys dist in their catalog with GM module on the side:" Allow your plug gaps to be opened up to 0.055"! DUI HEI dist ' 0.055"-0.060" plug gaps. Hmm.

It is true that larger plug gaps put more load on the ign system. That is why Plat/Irid plugs are a good idea because they take less firing voltage & you can increase the gap & still not stress your ign system. Other benefits that I do not think have been mentioned:
- the Plat/Irid tips run slightly hotter, burn off deposits that might otherwise kill the spark.
- electrons jump more readily from a hotter surface. By having the centre electrode hotter, it is encouraging spark formation.
- why do some P & I plugs also have P & I inserts on the ground straps? Because they are much harder metals & take longer to erode the electrode surface. Eroded electrodes means increased gap...& misfire.