Spark plugs tend to seize in aluminum heads more than in cast iron heads. I still use some anti seize when installing plugs in aluminum heads. When I was quite young I saw a plug broken off. I was able to grind down the top of some hacksaw blades to where it would go inside the threads of the broken plug. I made some cuts in the threads & was able to get plug pieces out without pulling the head. Screw extractors only expanded the broken plug in the head.
yes, the older style did sieze in the heads, but i had found that to be going well past the replacement times.
i think (but cannot swear) that back then, 60,000 miles was the replacement intervals. well before that, a customer would have a tune up yearly and that was (in most instances) about 18,000 miles.
i do remember a customer going about 3 years before he remembered he needed a tune up. i had to use a 1/2 breaker bar to remove the plugs, but that was also, a cast iron head...
i had always used a small amount of anti-seize on either engine i was installing them into. just made for good insurance.
The problems were with quite a few years of the Triton V-8s on the blow outs the plugs would take the threads with them making for a costly repair until the after-market sector came up with cutters and new thread inserts, then after that it had a lot to due with the plug design that cause them to break off, new designs have help that, lots of good you-tube videos on the subject.
yes, i recall that ford had some very angry customers back then. i personally only had the ceramic blow out of "some" plugs, leaving the metal housing still in the head.. it was a simple removal after that...
now, i am leasing my car, a 4 cyl camry. i may keep it at lease end, and buy it, or trade it in for a car that I WILL buy, rather than lease anymore.
i put on very little miles now, in fact, the past few vehicles rarely got past 90,000 miles, (that could be as many as 9-10 years of keeping them) and i trade them in.
so spark plug replacements, will not (or have not) been a concern of mine.
as it is now, you all know my sitiatuion with my back, so bending over the fender or grille to change spark plugs just ain't gonna happen, in spite of the fact, i still have many of my tools...