I remember back in the late 80's when a lot of the "Monster" cable stuff was just getting going for the home audio buffs. One of the higher end audiophile mags did a structured test between several different speaker cables all the way from the stock wire that came with the speakers to Monster Cables to 14 gauge zip cord (yes, the stuff you use to plug your lamp into the wall with!) to some really small, really crappy stuff they found.
They did three different tests if my memory is working, a double blind A-B test with assorted listeners, they generated a full frequency test signal with an amp, sent it down the wires under test and compared what came out with what went in on an scope, and then they measured all the parameters of each cable (resistance, capacitance, inductance, resenance frequencies, etc.).
The double blind listening test was very interesting. There was NO difference between ANY of the cables except the supper small gauge crap wire. On the measured performance, the winner was the (wait for it....) 14 gauge zip cord! All the hype about the low oxygen, low capacitance nature of the MCs proved to be bunk. It made no measureable difference what so ever. They also showed that the electrical effects of the cable were completely irrelevant to sound quality as well, as long as the wire was big enough to carry the power without inducing significant voltage drops.
The winner overall was the cheap lamp cord available at any hardware store for pennies a foot! It's even worse when you talk about digital connections. About the only thing you are going to pay money for (ok, SHOULD pay money for!) is better connectors that fit the plug WELL, better insulation (thicker, more flexible, etc., but only to a point!) and a bit larger gauge wire (only needed for long runs or high power analog signals anyway) or just a bit better construction overall. Most of the rest of that is just marketing hype.