The IMC Rating is a great and useful privilege to have. Unless one has a de-iced turbocharged or turboprop aircraft, it is probably nearly as useful as the full IR. I wish other countries had it.
But whether somebody can actually make use of it depends on several factors, most of which are not present in the typical UK GA situation.
You need to have a decent instructor, one who flies IFR for real, not just the usual type who gets you to do some NDB holds. These types are rare. An experienced IR instructor will have a very different perspective.
You need to get access to a decent plane, in which the avionics not only actually work but also have been properly tested and calibrated. Most school planes are not in this category because training is done in VMC, and even if you can find an instructor who will train in IMC, he isn't likely to be overly concerned that the VOR receiver or the ADF haven't been looked at for 10 years and the DME reads whatever it wants to. A panel mounted GPS is also highly desirable, as is an autopilot; these two will dramatically reduce the average workload.
You need to keep current, perhaps a minimum of 30-50 hours a year, with a fair bit of IMC flying within that. And the currency needs to be on the type, not on a variety of unrelated types, pottering about on nice sunny days.
The above requirements tend to mean that you need to either be an owner (a great way to get flying done, at similarly great expense
) or be in a syndicate whose other members are sufficiently solvent and committed to IFR flight to readily cough up when something in the panel needs fixing. Most syndicates have too many "VFR only" members and people who want to fly IFR tend to sell out before things get ever worse.
Re foggles, I am convinced that flying with foggles is much harder than flying in IMC for real. With foggles, one can't scan the panel properly while reading e.g. approach plates. With foggles one can also cheat easily; the proper "IFR hood" stops that but makes it even harder to scan, it is like peering through a pair of binoculars.
The IMCR transforms one's ability to fly from A to B at a pre-planned date, and come back as planned. My guess (looking at weather and whether I would have done it as a PPL-only) would be a 5x reduction in cancelled intra-UK journeys. This is true even though most of the said journeys are, on the day, done mostly or wholly in VMC. It is just that a prudent pilot would not have done them without the IMC option.
To significantly improve the cancellation rate, I would want a turbo or turboprop plane certified for known ice, and by that I mean something better than some dog of an old twin with rubber boots covered in stuck-on patches... and preferably pressurised. That's a load of $$$$$$$$$$. I suppose a TB21 with full TKS (£300k) would be the baseline.
Incidentally, with the IMCR, you can fly VMC on top over France. This option is very useful.