I've got em on my I4 and the fitment sucks more balls than an unattended vaccume at a retard convention.....reguardless i did feel a slight gain when i installed the nology wires and iridium plugs. Your dealer is confusing spark plug heat range with too hot of a spark.....im afraid he's a retard. Too hot of a spark plug heat range will cause detonation that will kill your motor...a good solid spark however will simply ignite the air fuel mixture better.
I installed the Nology hotwires and Nology Silver plugs and man, they're working out great. I had to trouble with the fitment. Only trouble was trying to get the wires alligned right so I could but the seperators on. Still haven't done that yet.