Just visiting this thread that got made while I was away last month...
My 2 cents on the CRX spoiler: unless it continues the taper of the body at the rear, it was probably designed more for downforce than lowering Cd. It's hard to tell from the pic, but to me, it looks like it sticks straight out, horizontally.
Still, it's similar to the cardboard junk I tried on my car:
95metro tribute: cardboard partial boat-tail prototype - preliminary results