From my observation so far, I don't believe expensive cables will always sound better. But I'm a cable believer by experience. I made many cables for my own experiments, and I do observed differences in sound signature just by swapping cables. I observe, differences mostly due to cable structure, coaxial, twisted, or braided. Material also cause differences. Easiest example is
DITA. Their IEM, The Answer and The Answer Truth Edition, are exactly using the same driver and housing structure. The only difference between the two is the cable. And that's enough to cause significant changes to the price. The sound signature between the two is clearly different. Not night and day different, but clearly different even by untrained ears. I had the opportunity last year to borrow both for more than a month, so I could clearly observe the differences. From the info I got so far, The
Van den Hul cable on the Truth Edition is interestingly not high purity copper or silver, but it is an alloy of many different material.
I was never a believer in cables myself, until I got to try a few top notch brands (Toxic Cables, PW Audio, Double Helix). They really improved the sound for me - a lot of it could be down to expectation bias, or the placebo effect. Still, some A/Bing does yield apparent sonic differences. Quite amazing, actually.