Erm, if the fact of increasing payments towards fixing you car because you were over the speed limit reduces the cost of insurance, then that is a benefit to the careful driver.
What it is more likely do is improve lawyers income with people arguing with insurance companies over the fact that just because I was speeding earlier, at the point of the accident I was driving within the parameters of the law...
What gets me is if they can put these blackboxes in, and my gps does this anyway, why can't they regulate the speeds of the vehicle on the roads. If you are on the limit, the accelerator doesn't allow further acceleration, except in short bursts (which is needed for accident avoidance in certain situations). Oh wait...the police department won't be able to fine any more.
This is merely a revenue generation type black box. If you're going to do it on the premise of saving lives, go the whole way or don't do it at all...