Rotorspeed - the problem with your advice is that it is too simple - if we just said to people before they went flying 'don't crash' it would have about the same effect as your 'don't go below 500' ie none.
In the harsh reality of the GA heli world people get airborne to do something (fly to see friends, have lunch, sightsee etc) and have had to make time in their busy lives to do it. Therefore many of them are unlikely to be put off at the first hurdle (crap weather forecast) as the met man is often wrong and it has got be worth 'giving it a go'.
Then, once airborne the pressure to complete the task and avoid disappointing others or themselves leads pilots into compromising their training.
Even if they started with a 'not below 500' philosophy' they will kid themselves that 'just this once' they can go to 400' just to get round the last bit of bad weather after which it is bound to get better.
Now it's really crap and having compromised their principles once, convince themselves that it is better to push on than turn back - completely ignoring the obvious evidence of lowering cloudbase and worsening vis.
Many pilots have done this and got away with it because the met man was wrong and it really was the last bit of cloud before the wx improved.
But if your luck is out and you keep pushing then inadvertant IMC is almost inevitable, made worse because you are unsure of your position and therfore that of high ground, masts etc and have no idea what your safety altitude is even if you could fly on instruments to get there.
This is how crashes happen.
If you don't believe people get airborne unprepared then why did I have to show an R44 pilot where his intended landing site was yesterday by flying over it and talking him on, because he hadn't checked either the contact frequency or the grid reference before he got airborne.
Unless the CAA mandates instrument training for PPLs, no-one will bother because a. they don't think IIMC will ever happen to them and b. it costs money and the CAA have already taken enough of that from them.