Well I was skeptical at first, but reading around it really seemed like the HD 650s seemed to benefit more from cables than other HPs... So i decided to pick up a used black dragon V1 for cheap (full retail for most of them is ludicrous IMO). And in all honesty... I heard the same things you did... still same sound overall... but just cleaned up and more on the ends (more punchy bass, slightly more energetic trebles). My stock cable was brand new basically... so not really due to wear and tear. Did some testing with my friend (also an engineer who was a cable skeptic) and even he couldn't deny there was a discernible difference. Just my own experience... YMMV
In the end... are expensive aftermarket cables worth it? Prob not for full retail... most ppl are better off saving for better amp or new HPs. But if anyone's feeling open minded and can nab a cheap cable to test out and try it... I'd recommend giving it a listen.
I agree too. I was a really huge skeptic in terms of cables but I did find a fair offer for a used equinox cable. I know all the cable talk is very controversial and highly subjective but unfortunately for me (more unfortunate for my wallet), there was a prominent change. The cleaner sound definitely changed my mind quite a bit on how HD650's handles EDM. Are these cables worth the $300+ price tag? That is up to each individual person. To me however, I think that is far too much of an asking price even if the changes were quite significant. If people can find these cables for a more affordable price however, I do see these as being something worth trying out. Otherwise save up or use the $300+ to go towards a great AMP or DAC.