I don't think I recall a single accident where someone inadvertently entered a spin when at cruise height and failed to recover
What is cruise height exactly? If you mean higher than in a circuit there must be some accidents like this or there would have been no argument to remove spinning from the syllabus in the first place. Unless we assume that all spinning accidents from altitude were intentional spins.
other than during aerobatics and deliberately mishandling the aeroplane
That's quite a bold statement. To me deliberate mishandling would only cover over-speed and over-stress or other out of envelope stuff which doesn't really apply to spinning. Lack of understanding can kill regardless of height if you are intentionally spinning... and there are always going to be those times that the aircraft does something strange and no one can explain why!
As far as what should be included in the PPL spinning is probably best left out because a student could have a 250 hour instructor that isn't competent to teach it! Even a demonstration might be a bad idea. That really sums it all up doesn't it?