You are so right Jim. I went through the entire thought process on this when I was doing my build. Initially it was kinda like "as an A&P surely I can make this better" and "all of the other (certified) planes I have worked one have turnbuckles". When I understood the simplicity of the Kitfox rudder cable system I realized there was no need for any "improvements".
When I put my rudder on I found that there was a slight difference in alignment of the pilot to co-pilot rudder pedals with the rudder centered. I decided to rig it such that the pilot's pedals were centered with the rudder in neutral. No one has noticed anything from the right seat.
Lastly on the topic of cable stretch with temperature changes. This is something I teach as an A&P instructor. It has to do with the difference in expansion of the different types of metal of an aircraft. Aircraft with an aluminum fuselages have this issue because the airframe expands & contracts at a different rate then the steel cables. On the Kitfox (or any steel tube airframe) this isn't an problem because the airframe and cables are both made from steel. There isn't any difference in the amount expand & contract.