Do it !
I think you have already aswered your own question, the IMC is about much more than tracking a few VOR's
I would hope that your instructor would bring in the use of GPS for IMC navigation and approaches if only to back up use of VOR & ADF.
With the changeable weather in the UK the IMC gives you the option of climbing above the MSA if the visibility makes continuing VFR impractical.
In short the IMC rating makes you a much safer pilot, I recommend it for any PPL holder who intends to go places.