hey
the mazdaspeed flywheel doesnt really do that much as it is not much lighter than stock (only a few pounds i think). the idea of a flywheel is to keep the engine moving. the heavier it is the more "stable" the engine is. the lighter it is, the more prone it is to stalling. ie - you have no flywheel, you have no idle.
but you can get about a 9lb flywheel from a few companies (like indigospeed) which would work well.
the idea of a lighter flywheel is to take mass off the engine. the less weight the engine has to move, more power goes to the ground and the engine is more rev happy. similar idea with underdrive pulleys, but a much greater effect.
hope this helps
later