In my opinion here is are some good reasons to purchase moderate to high end cables.
1. A interconnect is made up with many parts, one of the most important is the ends. Without the ends the interconnect would be useless. Stock interconnects have really poor ends that once placed on a connection usually spread out and if removed will never have the same grip. Usually more expensive interconnects will have a end that is cut to have a better grip or maybe locking ends, so removing them will not have the same effect. Another side to the end is the material that it is coated in, typically gold. Very few stock interconnects are covered with any non-corosive material.
2. The other part that is at stake is all cables that are designed to maintain a 75ohm impedance. Anytime the cable is bent or twisted and if the dielectric allows the center connductor and shielding come closer or farther away from each other the 75ohm impedance is altered. This can cause some of the loss, or allow unwanted signals to enter the cable ex: 115v. All high voltage cable will allow a ring of emi to follow down the line. if this emi is allowed to follow the interconnect, and the cable is not shielded, or the end allows it to enter the chassis, you can have some audible issues.
3. Cosmetics- Lets face it, some electronics are purchased largely by their cosmetics, now not all of the cosmetics are done for no reason. The wrap that is typically found on higher end cable can offer a non-wear sheath so cables will not allow the small vibrations to deterate the outer skin of the cable, and lets face it, it can make a really cool effect on the looks.