I think you'd find unmarked ninja cameras WOULD make a difference. Have you driven through the silly new tunnel? The cameras aren't marked yet, but people know they're there... somewhere. So everyone drives at 50-70kph. I've only ever seen three other cars do 80 through there. A Porsche, a Supra and another Skyline. I overtake EVERY SINGLE PERSON in that tunnel, doing 75-80kph the whole way.
If everyone knew that there would be unmarked cameras potentially ANYWHERE at any time, they'd all drive like nanas on every street. Yes, it'd suck that everyone would be doing 40-50 on main roads, but after the cops decide to fine them for going too slow as well, we should see a nice end result