>The Westy arrangement is almost the worst possible aerodynamics on a
Vanagon.

May or may not be true.  Remember that a hi-top still has more frontal
area.  One could streamline a huge truck, but it's still pushing a lot of
air, so a smaller vehicle with "worst" aerodynamics will likely still
slip through the air more easily.
And the "suction" off the back of a vehicle also affects aerodynamics and
a high top is likely a lot worst in this regard.

Having said that I stll think of ways to modify the Westy luggage rack
after seeing those win-tunnel pictures!

Happy trails,
John