To be honest, it's more about the MoT than being pulled by the Old Bill. The reflectors are a legal requirement but the R32 rear end solves that. The rest is a little bit more subjective and is down to the descretion vehicle tester or Police officer. So long as the colour and intensity (from a 'reasonable' distance) are considered to be ok, you should be fine.
With regards to fitting higher power bulbs, this presents two further problems. The first is the extra heat generated by high-wattage bulbs and the effect this could have on the lenses and bulbs holders. The second, is the additional current they will draw and the load they will place on the wiring, which could also potentially (I stress potentially, not definitely) melt. Plus, finding higher power bulbs with the right fitment could also be an issue and/or be quite expensive. Not sure how the computer system will cope with the higher draw as well - obviously it's designed to flag a fault when a bulbs fails (based on the drop in current being drawn). It might also throw up an error (and shut off the bulb) is the draw is too high as well? But this is pure speculation.
Having never really payed any attention to it before, can anyone answer why the R32 has reflectors in the bumper and the GTI doesn't but they both use the same design of light cluster?