Lets not get into another cable discussion here... yes, the cable on the DT700 is a bit utilitarian with a slightly sticky, rubbery feel to it, and replacing it with something that looks nicer, has the correct length and might produce less microphonics might be worth it. Beyer doesn't include defective cables with their headphones, so I'd rather not expect the sound to change to the better though. A broken connector is something different and reason for exchange.
Not trying a headphone because "someone on the Internet said" may spare you some money of course. On the other hand it's really hard to interpret someone else's experience to oneself. If its not just for curiosity, but for the realistic chance of keeping them, I'd order a pair and try out for myself. I did so myself, and the reviews almost made me cancel my order (or at least prepared me to send them back) -- which would have been quite a bad mistake. I really like them, a lot.
Regarding FR: Those Sonarworks diagrams are so compressed on the frequency dimension that they exaggerate level differences. They miss correct labeling for frequency. Aren't those the guys that sell software to make every headphone sound the same? OK, that was not nice to say... But somehow it seems to me that exaggerating deviations from a zero line furthers their business model.