I need some insight on specifically what happens at the plug when the gaps cannot be fired for any reason such as a very lean misture, excessive gap or a short.
The plugs have center electrode resistance anywhere from 500 to 5000 ohms.
Does the spark attempt to find ground to the shell in these cases, causing random missfires?
How does the voltage drop accross the resistance affect the outcome?

In the specific situation the coil is right on top of the plug valve by spring connection inside a rubber boot.
The coil resistance is 7000 ohms, the plugs are in the 3000 ohm range.
I am trying to track down the reason for random light load missfires that go away with a plug changes but return in a short time and go away again with another new set of plugs.
This last set was selected for lower center electrode resistance and still in testing stages.
If the missing returns, I am next going to replace the boots.
It may be the boots have grown in size and donot fit the plugs tight. As soon as the dielectric grease dries hard the leakage begins.
The coils may be pretty hot for voltage.

Sounds like you have a coil-over-plug arrangement -  One coil per plug.  If you can isolate the miss to one cylinder, you might try moving that cylinder's coil to another location to see if the problem follows the coil.

The coil will fire at higher voltage as the spark gap increases. The insulation in the coil and the boot are highly stressed with this higher voltage and can fail. New plugs can help for a while since the initial gap can keep the voltage below the level where the damaged insulation breaks down.

The resistance rating of the plug affects the RFI emissions that cause radio noise and probably not a factor in your problem.

One problem I see with all suggested solutions so far is that they suggest that the misfires are due to the spark occuring at other places than the gap in the plug. This tends to happen under high engine load, not no load, because under load there is higher pressure in the cylinder which then requires higher voltage to break down to make a spark. So that can't be the problem. I would guess that the problem would have something to do with timing or fuel mixture which changes between load and no load. Something about the plugs are changing so that the spark is not intense enough to ignite the mixture at no load conditions.
Perhaps the gap is too small?

If I have an ignition system based misfire only under certain conditions, I jump to the conclusion that those are the conditions under which there is the most resistance to a spark jumping the plug gap.

If a spark won't jump a gap, it will very often jump a smaller gap. If the gap is to small to generate a hot enough spark to fire the charge, it will still misfire. You then know whether it is an insulation breakdown, or insufficient energy to light the charge you have.

If the latter you then need to decide if you need to improve spark energy or improve charge quality.

The ignitability of the charge can be affected by any number of things, like A/F ratio, charge temperature, cylinder pressure at firing point, fuel distribution, fuel particle size, turbulence etc etc.

Cylinder pressure might degrade due to poor ring seal, lack of oil on the bores, poor valve seal, changes to valve timing due to cam drive wear or miss alignment or cam lobe wear.

Cam lobe wear is a common cause of a low speed miss. Regards

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