Not that it's a major effect, but it's actually the other way around, Finer. Higher resitance in a plug lead will make the spark slightly longer, but slightly lower voltage over the length of the spark - overall spark energy will be about the same. I believe what you're referring to is the air gap of the rotor button to distributor contact, and the spark plug air gap. Increasing the air gap will force the voltage (not current) in the coil secondary to reach a higher level before it can bridge the air gaps as a spark.I have been told (and will again no doubt) that leads with higher resistance tend to concentrate the spark to a shorter time. Ie the current is concentrated until it overcomes the resistance and can then flow.
In old 6 volt systems the jump gap principle was sometimes used to do this. The gap in the HT cable created a point of high resistence.
So if there is anything to this, a lead with a reasonable resistance might well assist the spark than would a lead with virtually no resistance.
Fact or fiction. Bring on the Myth Busters.
Plug lead resistance plays pretty much no part in anything until the coil fires a spark, and the coil fires when the voltage increases to a point where it can jump the combined rotor button and spark plug air gap. Once the spark fires to bridge the gaps, the resistance of the air gaps drops down from many meg-ohms (read bloody high resistance - way way higher than any spark plug lead) to the order of a few hundred ohms, as the plasma arc of the spark is a pretty low resistance.
Once the spark gap is jumped by a spark, the plug lead resistance then plays a part in minimising the peak spike of voltage of the spark, which minimises electrical interference.
As the Doc said with thicker plug leads, the actual part which carries the spark voltage is usually very similar in size and performance. The performance increase (if any) comes with the thicker insulation which does better to keep the very high initial spark voltage (10,000 volts or thereabouts, and much higher with CDI systems) from getting out of the plug lead, and into another plug lead or an earth point, which will cause a crossfire or misfire. It's a bit like ULP vs PULP though. If the stock plug leads are doing their job, then you'll get no improvement out of a thicker set of leads.
The best way to keep a coil ignition system operating effectively is to keep the leads, inside and outside of the cap and the spark plug itself bloody clean (NO grease or oil), and monitor the spark plug gaps and also the rotor button to distributor contact gap - any 'erosion' or increase in gap, then regap the plugs and replace the cap and rotor as neccesary.
Yella, carbon is very conductive - if you want to piss off a mate (who doesn't read this forum
) then get yourself an HB pencil, and draw a line across the insulators of his spark plugs from the top contact to the metal part of the plug - instant tracking to earth, and no go until the plugs are cleaned. 
