It is quite believable that huge towering Cbs would be embedded in other clouds. Even if the estimates were wrong and the clouds "only" went to 30,000 ft, or even "only" 20,000 ft, we'd be in trouble. Plus as said earlier, VFR aircraft are not equipped to handle icing. Airspeed would decay, lift would reduce, weight would increase, pitot would be clogged - not a good combination.
The PIFR is now quite flexible because you can add on approaches. You can start off just being able to climb through cloud, and at any time you can add on extra "bits" to it. There's a CAAP on it somewhere. You don't need to do the IREX exam for the PIFR.
I've actually done the Command Instrument Rating training. I just need a 4 more night command hours and I'm there. I know the Command Instrument rating does cover you for NVFR, I can't remember if the PIFR (or variations of the PIFR) cover this. Perhaps there is a night add on?
I did the NVFR training but never did the test - long story, couldn't find an ATO to test my instructor who was doing his approval test at the same time. Anyway, if you do an instrument rating it isn't necessary. NVFR training I found frustrating. Late nights after work and countless cancellations due weather after driving to the airport after last light. At least the IFR training is more likely to happen when you do night flights.
For a command instrument rating you can do a fair bit of the flying in the sim. I did some in the sim but most of it in flight - some under the hood, some in real IMC, some by day, some by night. The dark night IFR flights under the hood and in IMC were the ones where all the sensory illusions were most pronounced. Very tiring!