true, do not waste money on iridium or other plugs ..use only Orignal copper plugs with correct gap, provided by manufacturer..
spark plug gap is very much important. I have used iridium denso Ik 16 with gap,
0.6mm, 0.75 mm, and 1.1 mm, results given below,
0.6 mm is narrow gap, very good idling.
0.75 mm is little narrow gap, gives better acceleration than 0.6 mm,
1.1 mm, idling is not good as in 0.6 mm but accleration and speed is definetly improved.
summary: using iridium performance plug on 2009 to 2014 model , overall engine performance does not change although plug gap can cause variation in driving the car. but orignal OEM copper plugs are good for smooth idling and acceleration..