It all depends on you situation. For example:
1) If you currently hold a CAA PPL with IMC rating and multi rating and have passed the CAA ATPL exams it is definately worth doing. You do a 43 hour Multi IR course, then a 15 hour CPL course.
2) If you currently hold a JAA PPL with no experience on twins, your best bet is probably to do a 28 hour CPL and multi course and then a 50 hour IR course.
What's your circumstances?