Wow, what a thread.
Of course Fuji is right about the advisory nature of the IMCR DH/MDH. It has always been that way since the IMC rating was invented. When I did my IMCR there was no mandatory DH/MDH at all for non public transport flights, but now the IR minima are mandatory. The 1800 m vis is mandatory.
There are various ways to get IMC rating privilages in addition to a PPL holder doing an IMC rating course. For example a current airline pilot with a CAA issued JAR ATPL (not uk national ATPL) may want to put an IMC rating on his licence if he wants to fly a single pilot aeroplane on his days off. This he will get without need for training or testing assuming he has a airline LPC in the previous 24 months.
Should a current ATPL holder voluntarily restrict himself the advisory DH/MDH? Of course he would be advised to be in current practice with single pilot instrument flying before shooting approaches IFR for real.