I would offer a differing opinion than Grege that people who recommend cable upgrades are frauds.
I rely on reason, logic and evidence...not conjecture. Here is a simple, measurable, example that I experienced in my system. My amplifier was running hot to the touch. My friend Bill suggested we use some better speaker cables to lower the resistance. I was using some 12awg cheapie cables. So we bought Military Spec, 12awg, silver-coated copper wire, with teflon coating off ebay. Cost me maybe $60 total. Using a drill and a vice clamp, we twisted them ourselves.
We set up an SPL meter to measure any differences in sound level (at the exact same amp output, and same SPL meter location), before and after the new cables were installed. The simple change in cables resulted in a 3db increase in sound level, and the amp no longer ran hot to the touch. Where I used to run it at 1/2 volume...it was now at 1/4 volume for the same loudness. I won't comment on sonic differences, as that is subjective. But needless to say, there are measurable differences that cables can make in capacitance, inductance, and resistance.
I bought a Zu Audio Bok power cable for my subwoofer off ebay for under $100. Mainly because I know that when there is a dynamic sub signal, the resistance in my power cable won't be a bottleneck to getting ample power to the sub.
Then again...maybe I'm a fraud. :-) Test these things yourself and see.