The Honda Dream 2 is a motorcycle, so that doesn't seem a particularly applicable comparison. It may have a Cd of 0.10 by itself but with an upright rider that seems doubtful. The GM Sunraycer is a pure teardrop PV research car, far less practical than an Insight for everyday use. I like modding as much as the next guy -did a lot of it on an Echo. But from my viewpoint, whatever is done must be practical from an everyday use viewpoint and cannot permantently damage my valuable car. So, I suppose my objectives are a bit different from those interested in pure research.
Still, I'm an engineer and would love to have a workspace to build an Insight tail for testing purposes. I think an attractive and practical Kamm back extension could be built using this technology:
Using Fiberglass/Foam Sandwich Composite
Front wheel fairings would seem attractive, but if one carefully studies the details of what Honda has already done, improvements may be only slight. Wheels which are already pretty smooth, front wheel stakes, aerodynamically shaped openings at wheel rear. Taking on the disadvantages of movable fairings for potentially small improvement doesn't seem very practical.