If anyone cares to measure braking distance of corroded brake discs from highway speeds against that of bedded in new brakes, the result will evidence my point.
Unfortunately it is that same reason why many people often think the new brakes just fitted are an upgrade. Even rubbish quality new brakes will be far better than expensive old brakes which were in poor condition.
In short, don't necessarily go for expensive brakes. Being able to afford more regular disc changes will probably give more real life benefits. That said, more exotic brakes should give favourable results at high speed but lower speed stopping distances won't be much different.
Fruity, just curious, how would any disc reach a point where there is sufficient rust etc.. on it that it wouldnt be cleared with the first few uses on a drive? My current discs are down to minimum thickness, so about as far gone as any would be, but since the car never sits unused more then a few days, any surface rust easily gets taken off on the next drive.
The only way i would see a disc degrade to the point where the surface is permanently deteriorated that new brakes are a significant upgrade, is if a car is left sitting for months/years in a humid environment. Not really a concern for the average user.