So I finished my new front deflector design and took a few pics. I didn't get a good reading on my last HWY trip so I don't know if they measurably improved FE, but I've finally got the design right I think, as far as theory goes.
From the front:
From the angle at which I imagine the airflow will approach the deflectors (notice the inner side strakes bordering the wheel wells):
From the side:
Another angle:
This shows the little center section of the front undertray I covered up, and further back, the center engine bay vent which I removed the lip from:
Next up for mods are a smaller engine bay vent, revised grill block flush with the bumper, revised rear suspension arm covers, revised rear tire deflectors, revised mirror mod, and a trunk lid extension.