Having owned the Roadster screen and lowers, and also riding with the fly screen most of the time, I would say you definitely should remove the lowers during the Spring, Summer, and Fall here. The Roadster screen also seems to trap some heat in the rider area at a stand still, as the heat from the radiator rises and is guided straight to the rider by the wind shield. Moving takes care of all of that though. Riding with the fly screen, I really don't notice any heat difference compared to any other bike...
I have since sold the Roadster screen and lowers because I didn't really use them that much in the two years that I had them.