I wish that they had it where when you salvage something you can get it replaced at a cheaper price. It would make a lot of sense. I got two chairs from the dump and used them as is until I could afford to replace them. So I saved a bit of money, but my sims didn't like it.
Also, when you visit the junk yard for the first time, it mentions you can take the salvagable thing home and get them repaire. So I think, maybe they did plan for you to repair them, but then got rid of it or something.