I have been around since long before a "100,000" mile plug. I've seen a bunch of used plugs. None of them hold a proper gap for that long, none of them.
I change plugs when I buy a different vehicle, don't trust previous owners, or the mechanics. I use very good plugs, not cheap, and the ridiculous high dollar plugs.
Bottom line, the different plug materials are mostly for the ability to raise the prices, most do last longer, and 50,000 miles is well more than enough to achieve from any spark plug. The reality is that a spark plug simply needs to survive the environment, and the best power material for a plug is aluminum, not platinum or iridium, or copper, or whatever. Those materials trade power for longevity.
I've used aluminum electrode plugs that lasted 40,000 miles with little wear, but I have not seen any appreciable difference in performance from any plug. Don't quote experiences with changing any old plugs for any new plugs. All old plugs are outperformed by any new plugs. I prefer a reasonable priced quality plug, Motorcraft, single platinum, low cost, and change them every couple of years. My 99 Explorer has the newest Ford called plug that cost $3.35 each from my dealer. That's the most that I've ever spent for plugs, I see no magic in these either.
Spark plugs and wires are not mysterious components, do not let salesman talk you out of extra money not needed. Avoid cheap parts, and cheap wires, but they all should be replaced on a certain schedule. Good luck,