My interpolation of the CAA stats suggests that 1/5 to 1/4 of PPL holders have and IMC.
And all of the rest of them should get one. People dither over it then get very excited when they do it. Flying approaches, getting over cloud etc etc all great fun. Fifteen hours next to an instucuctor is no bad thing either.Its the next step up. You are also happier about flying in more marginal conditions.
Having an IR though is the dogs, transits in class A, airways and a night rating that works in europe and approaches to 200'. If you have the means I highly recommend it.