I've got wheels from 24mm to 80mm and weights all over the place. The answer is yes, they do make a difference. Everything makes a difference and those differences are additive. What some people may realize is that at some point you're happy with what you got for equipment and your fitness. Then you wander and see what can be tweaked. It's those tweaks, that may seem small to others, that can make a measurable difference. Maybe that difference is small but it's a difference. A little here and a little there and suddenly your TT time is down a minute or you use 30 watts less in a crit. Performance, technique, equipment and fitness are what we can affect so why not check it out? Big things are the sum of the little things. GL