Bad idea imho. When speed limits make sense to drivers, they reinforce the hazard and importance of the speed limit.
When they are abused, and the limits don't appear to represent the prevailing conditions, then drivers will tend to choose their own speed, and then their confidence in the signed limits is called into question... so when they are set sensibly because of real hazards, they may be ignored.
A given national limit road might be fine at 100mph one day, one minute, even for a brief moment, and the next 10mph may be too fast.
Thankfully, our roads are, all said and done, pretty safe, and that is with many thousands of drivers being caught speeding daily, and they are just the ones being detected. Everyone speeds, and most of the time it is totally and perfectly safe. We can choose safe speeds. Meddling with limits will only confuse those who have difficulty choosing safe speeds even more, be that too fast and too slow for the conditions!
Yet, all at the same time, we have more people dying of accidents during operations in hospitals alone, than on the roads, or dying of ONE bacteria type in hospitals alone, and many many times more from smoking and drinking etc etc... all these could be reduced much more effectively, needless pointless deaths!
Some road/driver education might help a great deal too.
Ah, they all cost money, while catching 'speeders' makes money

silly me :x