Storage is a problem for vintage, both sewing machines and furniture. Once the new arrive a few years later any item will often gradually move away from the heated areas of the house to loft and cellars, eventually getting tossed out. Not all luckily.
I've been thinking much like you Sunflowerzz, mostly because of a few Berninas. The Bernina 500 numbers (and up) seem all to have a few white plastic gears and yet they have been my favorite to work on, particularly a 730. My Supermatic has a one or two plastic gears too, and after 50-60 years they are often still fine (their motor pulley is more of an issue). As long as it can be repaird and the repair is durable and dependable I don't mind too much either. That said, I like those all metal gear machines, like my Singer 201, it runs so smoothly :- )