Hi Ian
Luddite could be right in that brake fluid could be part of the problem, and YES you should get your brake fluid tested for water and replaced when required. We have already done the twice in the Plus Six.
However there is nothing in your car's brake system that cannot be retro-fitted. The brake system is simply an collection of components that starts with the brake pedal and ends with the pad gripping the rotor. To rectify the situation short of ripping the whole system out you need a brake expert with considerable experience. As with your suspension problem you went to suspension design engineers, in our case Peter and Dan at SSL. You didn't just replace the springs or the dampers, but you fitted a purpose designed system. With your brake system it is not an simple as just replacing four complete assemblies. We may well have more than one simple problem so you/we will need to work through the whole system. YES starting at the end of the system by replacing the brake pads may well be a logic, simple and relatively cheap point. And yes you may well effect some improvement.
It's worth a CRACK!!
Kerry