The iridium and platinum plugs do have a performance advantage over the nickel plated plugs, but under most circumstances, it is not measurable. The thinner tip causes a more dense corona to form around the tip when it fires so it is actually a hotter spark, and it fires more reliably under extremes of the fuel/air ratios.
The iridium and platinum plugs may not be used in racing, but neither are the regular nickel plated plugs. The tips have a special shape that does not last very long, but then they are changed very frequently so long life is not a consideration.
Back in the day of points and unleaded fuel, 10-12k changes for plugs was common. The tune-up was an annual affair. But then oil changes were bi-monthly or 1500 miles back then. The lead was hard on plugs, oil and valves.