The colder plugs won't really rob you of any power, so if that's what you prefer then by all means. The only thing they'll rob you of is gas mileage.
Those platinum plugs were probably the sole culprit to the misfires, our ignition systems hate platinum plugs. Most waste ignition systems seem to eat them very quickly and develop misfires.
I log KR every month or two on a long drive, and if I saw significant KR I may run colder plugs, but I rarely get even 1-2 degrees. I've got basic mods like you, intake, HV3, plog, 3 inch downpipe. Once I snag some ER rockers I'll get a tune from Overkill and call it done, that's when I may or may not run a colder plug.
