Freewheeling sounds like a really interesting idea. I tend to just put the clutch in but my commute isn't very long.
I have been considering a couple of aero mods. Some bikes have aerodynamic seat covers behind the driver when there is no passenger. I was thinking about creating a seat cover that is the shape of a large tapered mail box to smooth out the flow behind me (and give me extra storage). I have also considered an aerodynamic backpack to smooth out the flow. If I make one, it will be hard sided and will have some sort of slide on shoulder clips instead of straps. Straps are a pain to remove over leathers.
My carbed bike gets 10 mpg less in the winter than summer so I am planning on installing carb heaters. Hopefully this will help. I was able to find some on a UK website.
I have also been thinking about weight saving. The cheapest would probably be for me to lose a few pounds but I was thinking more about rotational weight. One possibility is to move from 530 chain and sprocket to 520. I would also consider changing gearing at the same time.
A couple of interesting sites on motorcycle aerodynamics are:
Craig Vetter, designer and inventor of the Windjammer fairing and Triumph Hurricane Motorcycle - This is a great site if you haven't seen it already.
Ryno Fender - Expensive ($200) but interesting for sport bikes