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A wider gap, can create a hotter spark according to my father, he's an old GM tech. It may also effect the dwell time of the coil's before they fire, which would likely result in increased voltage and the hotter spark. But it can also result in a weaker spark. Depends on the system in question and the condition it is in.
I bet in most cases you would gain more torque by going with the OEM spec gap and advancing the ignition timing 1*
ETA: in 4cyl engines where the plugs are easy to change, personally I recommend copper plugs, (now keep in mind my background is performance engine related not mpg). They're cheap and seem to provide the most stable ignition under high load and high intake velocities, as well as excellent idle performance. They're also cheap, the downside though is they do need to be replaced MUCH more often. But at $2-3 a piece, I generally don't care or mind, I tend to replace them in my Talon for example every other oil change so, 6,000 miles. But it's a turbocharged engine that is flowing close to 40lb/min of air and much harder on the spark plugs than any mild mannered NA 4cyl.
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