I had an idea for a totally different and possibly sleeker version of front wheel skirts. I thought I'd post it here because I don't know if it is worth its own thread.
The idea is to use a stretchable fabric like spandex to flush-cover the wheel openings. Then, a frame is build around the wheel, attached at the knuckle/caliper (non-rotating assembly that turns with the wheel). As the wheel turns, the frame will push the stretchable cover outward. This would maintain a very smooth body shape, possibly even with attached flow the whole way.
The material would have to be climate-suitable. Maybe a stretchable neoprene would be an option?
If you've seen the BMW Concept "GINA", you'll get what I mean:
GINA
If this is worth a more lengthy discussion, mods feel free to create a thread.