I haven't taken anything I'd have to discard, so far.
I avoid machines with a ton of rust, I'm not ready to take something like that on (yet). Maybe some day.
I do have one machine (Singer 15) that's pretty darn rusty, first old machine I bought and I just snatched it up to play with it with no real goals in mind; I just thought it was cool and wanted to have it. I wouldn't buy it again it now that I know a little more, but since I already have it I've been slowly rehabbing it and replacing some minor parts. I call it my "learning" machine. I will probably never be able to make it look pretty, but I think I can make it sew again. Maybe some day I'll paint it.