Interesting choice you have, but a couple of ideas for starters:
What do you want to do with the rating? If all your flying is in the UK, then justifying an IR for the sake of being able to use Class A airspace might be difficult
Are you prepared for the ground exams? The 'Approved' IR requires you complete a (lengthy) ground school course, and for a period these were (and maybe still are) unavilable. The exams are a day and a half a Gatwick, something like four times a year, and are not trivial - you will need to do the course, or be very well read.
Can the IMC time be used against your IR? When I went trhough this, it was possible (there was an AIC that has now expired, but with all the transitional arrangements, there may be something in its place by now)
You will probably need an additional medical examination (aural) for an IR - if you elect to go for this rating, this is the cheapest hurdle to jump (and thus I suggest you do it first!)
Have you looked at joining
www.pplir.org ? There is a wealth of information there, and you maight want to consider advice from there.
BUt either way, (I did an IMC, used it possibly too much, and then did and IR two years ago), the skills you will get taught will sharpen up a number of aspects of your flying, notably accuracy of headings & heights, 'keeping ahead' of the a/c, working with ATC for mutual benefit, and so on....
Good luck either way, but the commitment to a UK CAA/JAR IR is significant in terms of both ca$h and your time.