Yet people spend £1000's on exhausts, wheels, remaps etc. etc. I don't see the negativity towards an improvement in braking for around the same as a set of 2nd hand LMGT4's. Making the car stop more quickly is surely more worthwhile than 90% of the performance mods people do. Your point about not being able to go faster than anyone on the street is true, so then if you're not tracking your car why not buy budget tyres, discs and pads as these would be perfectly adequate for day to day driving?
When you consider that you can pay ~£1000 for DBA discs and Ferrodo pads all round, another £500 for a BBK doesn't seem that crazy.