For the two cases that you have given, does it really matter? I don't know what the insurance rules are in your state/province/country. Here where I live, we have no-fault insurance so your own insurance company pays for all your damages and medical. You only need to sue the other side for extreme injuries that would keep you from work, but then again, if the crash was that bad I doubt that the other side hitting would be driving away from the accident.
The idea of having a rear-facing camera is novel, but I don't really know how much more it will actually offer. I guess it might come into play if you get a cop pulling up behind you and you want to document what they were doing. like did they come out with guns drawn demanding you to put your hands out the window where they can see them (or is that just on American TV stations)??
I also have come to the conclusion that for the most part, you want to be able to record that there was someone else involved, but it's not your job or requirement to be able to provide proof positive of who it is. Like, it would be fine to be able to show it was a Blue Sedan that sideswiped you, but it really doesn't matter if you can see if it was a man or woman driving, nor what the exact license plate was.