I found I can race with the big boys (ok, not the really big, 200.00 a car big boys) but the standard custom work guys, just by using my most broken in car.
Buying 10 tjet chassis and narrowing down to the 3 best cars, breaking them down cleaning them and mixing the parts around is usually enough to give you a great, smooth runner or 3. silicone tires, one thing I would do to smooth out the gears is smear them with toothpaste, then take the tires off, rubber band around the contoller and let it run for a while, then turn the car around so the gears mesh in the other direction. And silicone tires.
All I ever did. and in the last year I started buying rare earth magnets to glue in the backend of the uncontrollably fast cars.