A placebo effect is very powerful. I know that when I raced, I loved riding my bike with its superlight wheels and hand-glued tires. How much was the wheels, how much the tires, and how much the fact that I rode the race wheels in races, when I had rested before, was excited and generally in optimum shape?
Jim Papadopoulos developed a spreadsheet that calculates bicycle acceleration, so it should be easy to get some realistic values for power output, wind and rolling resistance and figure out how much faster lighter wheels accelerate.
In the mean time, the stories of professional racers trying and rejecting bikes with lighter wheels, like Saronni in the previous post, might be powerful anecdotal evidence. After all, the easiest way to make wheels lighter is to make them smaller. The current minimum wheel size is 550 mm, and a 700C wheel is more than 100 mm larger than the rules require. If it matters as much as most people believe, why hasn’t anybody taken advantage of this, and why have those who tried returned to standard wheels?
Reminds me of a certain 80 mile ride where a certain rider with slick carbon rims and hand-glued tubulars got a flat. Took them quite a long time, effort, and two people to change the tire.