Having just finished my IMCR, I can support most of the comments here.
IO540 is correct in pointing out the wide variances in the standard of instruction out there.
But seriously this is quite a huge issue. The IMCR syllabus is not as closely controlled as the PPL, the only gauges are the written exam (no mention of flight plans there) and the skills test. Guess what's not in that test either.
The net result of all of this is that the less willing instructors will teach what they know you need to pass, not what you need to know to keep yourself safe and unprosecuted. The flight plan stuff is in the Airlaw section of Trevor Thom and in theory at least ought to be known by a VFR PPL, but as with most things unless you use it you will lose it.
During the later flights of my IMCR, we tried to push the boundaries of the syllabus to add to my skills and knowledge. Likewise we went places and I accepted the additional charges of doing some ILS's at unfamiliar airports like East Midlands. Likewise, when my first few lessons were in an aircraft with single VOR/ILS and ADF, you really do learn how to navigate IMC with just the basics. Ultimately there are huge gaps in the syllabus so the onus is on the instructor to guide the student and for the student to ask questions outside of what is needed to pass the tests.
IMHO
Obs cop