IMO, the Fit has a poor Cd, as evidenced by its large frontal area, large side mirrors, and lack of any underbody treatment. Compare it to the 1st gen Honda Insight or the 1st gen Audi A2, both which had extensive aero treatments (including wheel, wheel housing, and tire) that resulted in very low Cd. It's also evidenced by the relatively poor fuel economy of the Fit at higher speeds (75+ mph), based on my own observations during a 300+ mile out-and-back trip I took.

I'm not unhappy with the fuel economy, nor do I care about the Cd, either. The Fit is still the best cost/safety/economy/utility car out there today. All automotive design is about balancing the compromises.

 

My question is how much do you think lowering the car down 1.5" all around would affect the cd? I would have to say it would help it wouldn't it?
Lower ground clearance = less air turbulence under the car...thus better stability at high speeds.
Is there a engineer in the house????

 

I don't think lowering has a noticeable effect on drag at road legal ride heights. It does benefit stability, but more because you need stiffer springs, and you've lowered the centre of gravity. It will help when you pass those trucks at high speed.

Downsides are speed bumps, bump steer (maybe not in a Fit) and bone jarring ride.