For *tone*, the only factors that make any difference are:
Guitar cables - capacitance. *Not* resistance - the resistance of a guitar cable is about 1 ohm or so at most; it connects a source impedance of a few tens of Kohms to an input impedance of a few hundred Kohms, so the resistance of the cable is completely insignificant. But the capacitance very much does matter - it's a few percent of the values in the guitar circuitry and *larger* than the input capacitance of the amp usually. It also acts as a simple resonant circuit when combined with the inductance of the pickup coil, so it actually 'tunes' the sound by changing the frequency and height of the resonant peak slightly. The capacitance is responsible for the genuine and easily audible differences in guitar cables. (It's also directly related to length, so short cables inherently have less capacitance than long ones.)
Speaker cables - the quality of the connectors. The capacitance is irrelevant in a non-shielded cable and the resistance is still too small to matter compared to that of the speakers. (Assuming the cable is at least of adequate gauge.) But the connector quality can make a small difference - cheap connectors can have flimsy parts and too much contact resistance.
Power cables: none. (Assuming at least of adequate gauge.)
These are all provable with blind testing or direct real-time A/B switching, no matter what any snake oil salesmen will tell you.
The quality of the cable and the way it's made can make a big difference to the reliability though.