Whilst you don't have to hold a CPL or ATPL to hold a CIR, whether you ultimately decide to go for the full Rating or just the PIFR, you need to approach it as a professional qualification. By this, I mean no Mickey-Mouse or cowboy-style "she'll-be-right" attitudes. I've said this on another thread, but you'd be amazed just how undisciplined and lazy it's possible for a VFR/PPL driver to be - and still manage to get away with it. In contrast, when you're in the soup with the expectation of having to fly an approach all the way to minimums before getting visual (if at all), you either get it right - or end up a statistic. There simply is no margin for error.
I'm not saying that you're a hack (in all fairness I don't know you, so I'm not judging), but I've met quite a few drivers over the years (recreational and professional alike) who have absolutely no business being at the controls of an aeroplane for IFR operations. The important distinction however, is that it's not the licence which determines how professional you are - it's your attitude.
Whichever one you go for, as long as you treat the Rating with the highest level of respect and don't push your luck too far, you'll enjoy some great flying.