Cars: Some cars suit an individual's driving style better than others...
I was unhappy with the way my Mugen turned, got a Losi, and got faster. Was unhappy with how hard that was to drive and with the wear, got a Jammin and got faster. Note that all 3 of the cars I mentioned are GREAT cars...
It is all about having a car that suits your style (and in my case with the Losi, skill level. It was too much for me.)
Will a modded motor make you faster? Some people MAYBE. Not me... I have more power than I can use already. I've never said "I wish it had just a hair more power" unless there was something wrong. Now a fuel mileage mod... hmmm...