Sorry -- my last email got sent before it was finished!
The bottom line is that any weight anywhere only increases the force required to accelerate the bike and the force required to climb up hills. There are other reasons why lighter wheels feel livelier, such as reduced gyroscopic effect which will be noticed when swaying the bike as you climb out of the saddle. Going from a heavy to very light saddle gives a similar sensation of liveliness under the same conditions. The benefit is largely psychological -- but that is always a major factor in sport. If you htink something is faster, it probably is.
Hugh Thornton