For me, a vintage will last a lifetime and beyond, simply because of the craftsmanship involved. Back then, it was all cast iron and metal, nowadays, everything is aluminum and plastic. My sister has our mother's sewing machine, a Singer before it was called Singer and while it is in desperate, desperate need of a good cleaning and service, it still runs. My guess is early 50s.
My Dressmaker is at least 45 years old and after some TLC from me and my serviceman, she runs like a champ and purrs like a kitten. I never, never give up on a machine pre-1980.
I now have a computerized machine and while I believe it's well-built, I know that she won't last as long as my Dressmaker or my mother's machine, even though I clean her religiously and oil the correct spots when its time. Because of the longevity issue with her, I may just keep her to simple sewing tasks and piecing my quilts, but anything heavier than that, I'll take it to my Dressmaker, including free motion quilting.
I've always had the belief that when you buy a sewing machine, no matter what you're buying it for, it's an investment. If you learn everything you can about your machine, do the simple task of cleaning it regularly, oiling it when it needs, taking it to a serviceman at least yearly for a tune-up and not push the limits of the machine itself, you can expect your machine to exceed the actual lifetime. If you don't take care of it and expect it to handle something that only industrial machines can handle, then you're only to fault because you didn't take care of it properly.