The IMC was invaluable for me, I recieved a a fantastic grounding in all the principles required for the IR (down to an excellent instructor I may add). It was also one of the reasons I passed my MEIR first time in minimum hours.
I completed my IMC rating before I started hour building in earnest, and whilst I never used it in anger, it certainly gave me confidence during a months hour building whilst flying 80 hours in the Scottish springtime!