I have old steel feet that are from the 19 teens that are wear free. I some others that look like someone took a grinder to them.
I do not have any of the newer aluminum ones that have much use on them at all. Well, my 1/4" foot has a bit and the plating is already wearing through.
The feed dogs are made from some pretty hard steel in the older machines. In the newer ones I don't know. They might be aluminum too for all I know. I know Singer made some from plastic years ago.
I suspect they'll all last a good long time if you don't run the machine past the end of the fabric or let somebody play with it.
Joe