The factory build used the tab washer, at least on early motors. Mostly you see them without the washer, which may depend on the number of cam or gear changes that have been done -- the tab breaks off after a few cycles of being bent.

The washer has zero affect on endplay or wear, it's just there to keep the nut from backing off. Loctite is strongly recommended if you don't have the washer.

I've only ever seen brass retaining plates, and I've seen them show no measurable wear even in high-mileage motors. If they plate is flat, it's bolted onto a clean surface, it's held in tight, and the spacer is on the cam nose, it should last as long as anything else in the motor.