Are you the type of person that modifies for looks or for performance? Some people like to keep the stock performance and just make it look unique while others like to enhance the performance of their vehicle no matter what it is. Which one are you and why?
ive allready spent MUCH more in the aesthetics department than the handling,ive just got the rear sway bar install and dont see myself doing any more than that,IF a well suited cold air intake becomes available i WILL get that,but would NOT expect much if any powere gains from the application,again it would be more for looks and sound.so my answere is aesthetics,like i have said many times,if i wanted to purchase a sportier ride,i would have spent 1000$ LESS and bought just that,eg,mazda 2.peace,have a great weekend all.
There's really not much you can do yet to an iQ performance-wise, without getting all rocket-science and fab-shop custom. Being a one-off of a Prius, the power train comes tuned fairly tight from the factory, with most the fun engine computer codes locked down. I have a cold-air intake, but I got it for free. I'm getting a muffler tune for sound, not for speed. Sway bar, lowering springs: the end...until a turbo or a supercharger kit comes out.
Mod for looks? Sky's the limit.
I don't see looks and performance as incompatible, until you go for "art car" and start cluttering up the aerodynamics. Compared to your butt in the driver's seat: short of armor plating aesthetic mods really don't weigh (sorry: have to say MASS) much either. Nothing but your wallet and schedule says you can't have it all.