The spark does not "burn" the fuel, but ignites it. The fuel burns when an ignition source is used and O2 is supplied. I agree that spark distribution can assist in ensuring complete combustion, however I am not sure that cutting the electrode back is the answer.
"Lots more horsepower and better fuel economy..." I really doubt the HP claim. Most modern engines are running pretty near design peak.
1998 C230 "Black Betty"