There are definitely differences in audio cables, but can we hear these differences? The test should be easy enough.
Tyll Hertsens over at InnerFidelity.com is working on something regarding cables so keep your ears open.
As for measurements these tests can also be done. Many cables I see in the market have claims, but the only measurements I have seen that make sense are the instantaneous current draw curves. Different cables differ by up to 50 microseconds, but I have no idea whether I would hear that or not. The simplest test is to to the cable swap yourself or record something through each cable and see if you can hear the difference in playback. Better yet do the old inverse polarity trick and add the two together.
Most gear I have tested sounds very similar especially DAC units. I have had a few amps that sound different, but I expect that from an amp more than a DAC. The amp controls the speaker after all and impedance becomes such an important roll at that point.
There are honest people out there that say they can hear the difference which means we should be able to as well. There is no doubt that the standard cable upgrade is one of the easiest ways to increase profit and I hear people doing it at audio outlets all of the time who have no right to say it. I usually go with a well built cable and leave it at that. Take my PBJ RCA cables. They cost $100 or so for an RCA cable, but to me it was worth it because I have had so many poorly made RCA cables that are noisy or have poor connectors. Now spending more than that depends upon budget. You can look at it another way. If we had unlimited funds which cable would you buy knowing nothing about actual sound quality? You would tend towards the more expensive because you assume some of that cost goes into labor and components. In the end we all buy what we can afford and what we like.
Sound quality is more of hobby for many of us and in the long run it is more about the journey than the results in the end.