Simple enough, plats are 50-70K plugs, iridium are higher or 100K, when they came out is when you first began to hear of the 100,000 mile first tuneup as predicated by Cadillac and others of the time.
They on the contrary told us to push E3s but they came back as fast as they went out.
I look at them the same way I did Splitfire and other gimmick plugs, overpriced garbage. Dad taught me that back in the '60s while working on his 8 bbl. '64 426 wedge Mopar, he had bought the latest 'trick of the week' plug or Fire Injectors, pure crap plugs. Esentially a surface gap plug that then ran way too cool to foul. He tried to run them for like two days, came home one night and yanked them all and threw them out as far as he could in the back field. I'll never forget that.
The true spark plug improvements? The fine wire platinum (notice they rip you off now, none are finewire anymore, only a spot of metal on the end), and iridium. Double plats if you run waste spark systems too. All else out there plugwise is garbage. Bosch +2 or +4? Garbage unless car came OEM equipped with them.