One thing I wonder is whether the people doing this will ultimately succeed.
If we will simply given up because replacing the cameras is too expensive and we don't have the means to catch these people.
Here in Cornwall, the police put out several statements asking if they would please stop, because it's awfully mean, and it costs the public purse money to repair them. I would have though the desperate tone of their messaging would simply encourage people, knowing that they have no real answer to the people doing the damage.
Hard to say how it will pan out long term, there is only so much the public will put up with before they start smashing or painting cameras and signs in the middle of the night.
And i think if the Wales example is rolled out UK wide then it wont go down well, 20mph is awkward. Im forever having to look at the dash since lower gears are very sensitive to light changes in pressure.