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As alluded to earlier, the reason blunt leading edges do better than one might expect (and better than sharp ones) is that, in subsonic flow, pressure changes can propogate upstream, so that the air ahead of the vehicle "knows" what's coming, and starts to get out of the way BEFORE the car arrives. For supersonic flow, the air just sits there, fat, dumb and happy...until WHAM! it gets hit by the solid object. Thus, you NEED a sharp leading edge to "split" the air.
Also, regarding Cd increase when a sufficiently aero shape is being drafted...consider a "good" airfoil (that has laminar flow ~2/3 the way back) that suddenly has a flat plate (worst-case scenario) placed just behind it. Assuming subsonic flow, the air will "know" the barn door's coming, so it'll start to get out of the way early. I virtually certain (never ran the tests, though) this will play hell with the laminar flow, and probably even attached flow, tanking Cd and lift.
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