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Phil, I thank you for the obvious investment of time you have made on this question. As you say, both Honda and Toyota may have "left a bit on the table," but as modders, we are pretty much stuck with their rear body angles. We aren't likely to be able to make changes there. Still, in the interest of science, it entirely appropriate that we try to figure this out.
I want to do more reading, but I'm somewhat suspicious of some of the older Cd data like that of Lay, Jaray, Kamm and Mair. (Please remember that skepticism is one of the cornerstones of science. It motivates us to challenge the conventional wisdom.) The numbers they provide, .15-.17 or so for bodies WITH WHEELS has just never seemed likely, in light of the insight's .25 Cd. Remember that these folks were in the business of selling "streamlining" and their incomes depended greatly on low Cd numbers. In addition, instrumentation wasn't nearly as good as current, and even Hucho has commented on this issue. Some of the "reasonable" data has been verified by Hucho, in the modern VW windtunnel, but other data such as the Tatra(if memory serves) did not stand up.
Here's and interesting example of the "marketing" problem. I have build and raced small sports cars. Of late, dyno testing has become all the rage. On the Dyno Dynamics chassis dyno, there is a software variable, this allows the operator to "correct" the power output for various "errors" which the operator perceives to be in play. The operator who adjusts the "correction" to the high side gets more business than the operator to sets the variable to a lower level. The car owner is much happier if his result says 110 hp vs. 106 hp, though nothing has actually changed!
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