A couple of things that come to mind looking at your plugs is they appear to be way too hot (long). This can really screw up your piston crown. Even worse if the motor is running lean. It can burn a big pit in the top of the piston, you can see it if you rotate the motor so the piston is near the top and look in the spark plug hole with a flashlight. For some cylinders you may need a small mirror.
And about the multi electrode plugs, once the fuel ignites (with dwell figured in), what difference does it make what the spark does. More spark, hotter spark, how about enough spark to ingnite the fuel in a predictable manor.
Much of the design of a head is the shape of the crown, the depth of the plug electrode and dwell. So the fuel burns in a predictable configuration (swirl). They actually configure heads, to enhance the burn. The design figures in the recommended plug.
I've had my XJ's run just fine with 0.060 gap (neglected them for way too long), I really can't see how adding another electrode is going to enhance performance much, but may likely screw with the design parameters a bit. I know my XJ runs like crap, with the Bosch multi electrode plugs (my Renix came that way used). Seems like the uneven combustion between the cylinders, due to my slightly different compression ratios between cylinders, becomes magnified with the Bosch multi electrode plugs.
The multi electrode plugs were originally designed for overhead cam motors, that often leak oil into the cylinders from the top. The multi elelctrode plugs, seemed to be less prone to fowling. There may be some benenfit, if you idle a lot.
Over here in Europe, a lot of guys have fried pistons, running hotter plugs (or even stock). If you are going to take advantage of the no speed limit autobahns, a colder plug actually works best and the motor lasts a lot longer. Running anything but the recommended plug (or colder) is asking for grief.
