In general, more mass in the crank damps vibration, and also lowers the frequency at which vibrations and harmonics occur.
Depending on the track, chassis etc. less weight may not help, especially with dirt.
On a time-to-speed dyno a lighter crank will develop more power every time at every speed (unless the valve gear can't keep up).
The improvement to the chassis as to acceleration will be roughly proportionate to the square of the overall gear ratio: 1st gear × axle × tire OD. If you go from a 2.20 1st gear (Muncie close 4 speed) to a 2.52 the change is over 31% - but only in 1st gear (the accel won't be 31% better, only the power loss due to speeding up the crank will be better).
You can also see from this that 1st gear is far more affected than 4th, by 535% (2.52^2 ÷ 1.00^2), which is why cars that race in high gear don't feel much different.
