Actually change of Air filter, Motor oil, gear oil, cleaning of Throttle, and other things involved that's why the slight pick increase may not be associated with plugs alone. but it does matter though. if the millage is good than you can elaborate that maximum fuel is burning due to good spark thus giving good power and pick.
My AC is loading up the engine significantly, this problem is due to AC, without AC my car millage is good so the pick, but with AC the pick is pathetic with low millage.