Getting untaxed and therefore probably uninsured and unroadworthy vehicles off the road would do a lot more for saftey and motoring costs than speed cameras do.
With some authorties removing speed cameras altogether perhaps a better solution would be to convert all speed cameras to ANPR cameras and catch uninsured untaxed vehicles and possibly unlicensed drivers.
With modern technology the Cameras could be linked by radio to the national computer and a message sent out to police vehicles in the area of "suspicious vehicles." a patrol car in the area could then intercept and investgate, assuming it wasn't on more important business.
speed cameras could then possibly be replace by flashing "overspeed" warning signs.