The cable manufacturers would have us believe that the best cables are made of silver, the next grade being oxygen free copper and the cheap cables of ordinary copper. The reason they claim is that better conductivity leads to better sound quality.
Sadly this is mostly nonsense as the conductivity of the purest oxygen free copper is only 1% better than the most common oxygen free copper, which would make no audible difference.
The main reasons for getting a good cable are build quality, convenience and aesthetics. Basically OFC cables tend to use higher quality plugs and solder and just look better. Silver cables can also come in handy as they are usually thinner and lighter than copper cables.
Once you have a cable that uses high quality components and is competently constructed, then there is little to no reason to spend more money on a replacement.
The only reason I would get a replacement cable for my HD650s is if I broke the standard cable, which is already high quality OFC or for convenience, in that I usually sit less than a metre from my amp, so something shorter than the standard 10 footer would be nice.
Only place that silver, etc. really has a potential to make a difference IMO is in the feedback loop of amps and stuff like that where short, high quality, traces/interconnects can significantly reduce noise and distortion (or rather poor quality can significantly increase it). You'd need significant resistance in an audio cable for it to really become a factor.
their answer was just to replace the whole headband rather than actually fix what's there.