IMHO the IMC is not necassary.Especially if you are going to do the CPL/IR at the same time (ie not having a break in between)
It is another £???? to add to the equation.
Dont forget it isnt valid outside the UK!
Me personally i would use the money you have for the IMC and spend it on the Hour building!
I know people will say it helps to have the experience of flying on instruments, but IMHO you will get some good experience on the CPL course!
Im going to do the Atpl full time. Ive already got my 50 hrs before.
I will complete the other 50 hrs after ive got the ATPL's passed.
By doing it this way i know i will be fresh when i get to the CPL & (FIr in my case!)
I hope this helps
REMEMBER this is only my opinion and might not suit everyone!