Cold solder joints and oxidization of connections will increase resistance. When I was a heavy smoker, the tar that coated my electronics led me to a lot of potentiometer and connection cleaning. The gauge of wire only matters if a cord was only made for a too low ampacity, say 500 ma.
Fer instance, 18 gauge wire has an ampacity of 6. 12 volts or 120, it will carry 6 amps at any length without overheating the wire to failure. Ah but resistance is futile. And the voltage drop can become too great for operability.
Another problem with some cables is that because the bezel on the nexus 7 juts out past the jack, a longer plug or trimming the plastic may help.