Just to edit something on my previous post, if you do the ATPL exams, I think you do have to do an approved groundschool course if you are converting your CPL/IR to a JAR CPL/IR. Bit irrelevant though as you're going to need some study anyway.
Lee - I think that converting a CPL/IR (H) is almost identical to converting your CPL/IR (A).
As for whether it's worth it, it's quite a task now to convert to a JAA licence so probably best avoided if possible.