A CPL is a CPL. Until you've met the requirements for an ATPL (1500hrs, 500 multi crew, etc etc etc), your CPL is EXACTLY THE SAME as anyone else's. The exams you took make NO DIFFERENCE AT ALL until you meet those ATPL requirements, at which point you are eligible to take an ATPL skills test. The "Frozen ATPL" myth is really quite irritating. There is no such thing. A CPL is a CPL, and an ATPL is an ATPL. "Frozen ATPL" means that one day, maybe, you might get an ATPL. Until that point you have a CPL just like anyone else.
Also, an MEP is largely irrelevant for instructing... until you've acquired sufficient experience to teach CPL students, at which point teaching multi might be useful.
I would certainly recommend an IR to anyone who takes their flying seriously. To those with little or no flying experience it's difficult to explain its value, but take a trip up with an instructor sometime and fly into cloud. Try something simple, like keeping straight and level. You'll soon realise how valuable instrument flying skills really are.