I would like to add some data to this study if I may. I am pleased to confirm that new wheels are faster; I conducted my own experiment today. On Thursday my wife gave me a Shimano RS81 wheel set for my birthday which I have only just fitted this afternoon. I went for a 10 mile spin with an average speed of 16.5 mph. Hampered by the fact that my dérailleur was a bit out sync which slowed me down a bit. However out of the last 25 rides I have only gone over 16.5 ave twice. So further proof if proof be needed that new wheels are faster.
I may add that new wheels also make you look faster and more attractive to the opposite sex, but that should go without saying.
Oh yes, and they also stop faster too, I nearly went over the feckin' handle bars. No one ever tells you about that do they?