Coming to sewing machine appreciation late in life I can say I totally misunderstood the beauty of sewing and sewing machines. Early life I was taught to "leave that machine alone. I have it the way I like it, so, don't bother it." Now I realize those words were uttered by people who did not understand the process involved in stitch making.
Back to OP, Miriam, you covered most attributes of vintage collecting, but the one I like best is there is a beauty beneath that ugliness. Most, if not all, vintage black machines can be brought back to a beautiful, working machine.