The speedster tail is purely an appearance option. It adds symmetrical wood ribs to the vertical stab, rudder, horizontal stab and elevator to fill them out and make them look aerodynamic. There's no effect on performance. In the grand scheme of building a Kitfox, installing them is fairly trivial; a few days at most.
Depends what your time's worth (the PVC fairings take time to fit, install, prep and paint), how concerned you are about weight (the chomoly struts are heavier), whether you want to be able to push your airplane around by the struts, and how price-sensitive you are. I'm putting $2 "NO PUSH" decals on my PVC fairings and using the $3,500 for fuel.Also the Chomoly Streamline Wing Struts. Are they worth $3500 in your opinions?