I also have to agree with a couple of points already given. Learning to drive smooth with your throttle can make a big difference in fuel economy and corner speed. A local racer who is very fast can get much longer runs for each of his tanks because he's smooth on the throttle even while being fast on the track. Alot of people pick up throttle blipping hard acceleration as a bad habbit that eats up extra fuel and sometimes can add time to your laps. All this can add up to less fuel stops and faster lap times.
In addition, 1/12 on road also teaches you to drive fast and smooth on the throttle to keep up and last with only 4 cells. It also quickens your reflexes to a point and can make you a faster driver.
2wd off road can also make you faster due to what others had mentioned. Learning to drive with more power than you need can always help you to drive better, faster and more smoothly.
Another thing is learning to use brakes and when to use them. Alot of drivers also had issues with using brakes and when to use them. Also, how to setup your brake bias to suit your driving style and track.
Good luck.