IR, this year. I found an instructor who has both JAA and FAA ratings so he can teach it in my G-reg.
Once a plane goes N-reg, your IMCR becomes worthless (any IFR ops in an N-reg require an ICAO IR).
Your JAA/UK PPL becomes limited to day VMC only, UK only. So one needs an FAA PPL at least if flying an N-reg plane; not being to go abroad isn't very useful, generally.
I use the IMCR privileges a lot, certainly on >50% of flights. BUT this doesn't mean one flies in IMC all the time, or even much. It means one can do a flight which, on any prudent assessment of the weather, could never be done on a plain PPL. With a plain PPL, anytime there is actual or forecast cloud below the MSA, you can't go. In the UK, this alone means cancelling more than 50% of previously planned flights. With the IMCR, one might cancel perhaps 10-20%. On the day however, one often ends up in conditions which would not be actually illegal for a plain PPL (in sight of surface, basically
) It is just, as I say, that a PPL would (should!) never have gone.
Ocassionally, one departs into muck and sees nothing until coming out on the ILS at . But even if one is doing that, one might be VMC on top for most of the flight, which is pretty nice.
The usefulness of the IMCR depends on whether the destination has a useful IAP, and on the icing level. If you fly only into grass strips then the IMCR isn't likely to be very useful; the option to fly VMC on top is great but nobody should recommend with a straight face that somebody does that while not being able to fly an IAP at the end. If you go into larger airports, especially ones with an ILS, then it is the best single thing you can do to help your flying (apart from buying your own plane
).
The IMCR is worthless abroad for IFR although (there is some dissent on this one but the CAA have confirmed it in writing) having it does remove the "in sight of surface" restriction on the PPL, allowing one to fly VMC on top in a lot of places. One has to get down somehow of course, and legally without going through cloud. In practice, this offers some leeway regarding acceptable weather even outside the UK.
As a safety enhancement, instrument flight is unbeatable. Far safer above the MSA, in IMC, especially with a decent GPS, than below the MSA anywhere.