This is such a subjective personal thing...
my butt dyno is insanely tuned to notice many small differences.
10hp is uber noticeable, ever turned on A/C or had it on while trying to merge on the freeway? In Civic's and Fits, I really, really notice it

.
From what I have read about the Fits throttle response or "feeling", it sounds as if it would be very worth an intake.
Springs would maybe be more bang for your buck as you get looks and perfomance that are less subtle.
intake-maybe more comfortable performance (subtle in feel and/or mental), low end and or high end. Possible savings in MPG...if driven for MPG sakes? looks good in the engine bay....errr at least different

. Most likely a drop in general MPG?
springs- maybe less comfort in everyday driving, might make your car look better if you like the drop look. Better performance if geometry is
maintained and/or pushed to notice. problems with ground clearance may occur, problems with rubbing may occur (mostly wheel and offset choice issue though)
neither of these things will make you a super hero but its the one that you will enjoy the most as the driver. And you can always change these things for a trackday and/or auto-x. If it gives you more confidence or more enjoyment...then...chances are you will (performance wise) gain alot more than what they are worth.
idunno...you seem
so torn...maybe get a nice quality but cheap version of each. Or save up more...all done up at once and you might actually feel
a HUGE diff, and ya never know what that might lead to...
If it was
strictly for performance only then get a good set of springs and call it a day. How much performance driving do you do and or really, really care about?
chibuki - Thanks for saying that... (not to sway either way) but alot of cars dont handle as well as the fit even when springs are fitted to them.
(and i have been unable to prove as of yet if lowering your ride really gets you the chicks....)