I think it won't. As you know you lose low end torque with a lighter flywheel, which will result in more wear of the clutch (especially in traffic) as the driver will have to let the clutch slip a lot more to prevent stalling the engine. To my knowledge ultralight flywheels only make sense for ridiculously tuned cars or racing cars which have a very narrow powerband at high revs.
Changing to a light weight flywheel will result in increased throttle response at any revs as less power/torque is wasted on getting parts to spin. You will therefore notice an increase in torque at lower revs. It would be a good idea to mate such a modification to an uprated cluch as the standard item would be over stressed by the increased engine response. One downfall to light flywheels is a faster decrease in speed when off the throttle and on inclines due to the loss of momentum over a standard weight flywheel. One alternative would be a carbon prop shaft....very expensive!
I concur with Okitenik,
For the best gains a flywheel must have the weight removed from the outside edges and thus reduces the loss of forces from the engine getting the flywheel to spin.
You should get a noticable improvement in acceleration - especially in lower gears.
'A Nissan Skyline GTR with a flywheel reduced in mass by 29% resulted in a measured improvement in the rolling 60-90km/h time from 1.8 to 1.7 seconds.' 21st Century Performance, Julian Edgar