Most of the spring upgrades will lower ride height, improve cornering performance but increase ride roughness to some extent.
Koni FSD shocks replace your stock shocks and work with stock springs to keep ride height but improve overall performance and ride quality.
See
http://www.tirerack.com/suspension/tests/koni_fsd.jsp
http://www.tirerack.com/suspension/s...FSD+Damper+Set
I don't see the Honda Fit on the list of applications for the Koni FSD.
I know that MINI owners are very happy with the Koni FSD for street use.
Try calling
Jim@tirerack.com to ask about Koni FSD for the FIT or for any other shocks tirerack sells that might also help your ride quality and handling.
When I search at tirerack.com for the FIT/ FIT sport I get only-
Eibach Pro-Kit springs $205
Ave lowering front 1.6" and rear 1.3" (moderate lowering)
or
Eibach Sportline springs $189
Ave lowering front 2" and rear 1.8" (extreme lowering)