Aero rims are important if you are a professional rider doing time trials but for everyone else the air drag is provided by the rider. Few bikes even have aero bars and this is the best place to start if one truly wants to reduce air drag. Pro racers realized quite some time ago that going from 23mm to 28mm tires had no discernible impact on rolling resistance but did smooth out the ride and in some cases the much lower tire pressures provided for less rolling resistance with the tire better able to roll over bumps in the road.