I would suggest looking into CorkSport accessories for minor engine mods (air intake, exhaust system and the like.) They have good products and their customer service is awesome. They also sell lighting kits that replace the stock bulbs with LEDs that are a lot brighter and crisper than stock.
There are a few different brands of coilover kits and springs that will lower the car a little bit and make it look sportier. I'm ambivalent about doing it myself because I already struggle with not having enough ground clearance thanks to the roads around where I live sucking and there being half a foot of snow on the ground.
New tires are good for a performance boost as well. The stock rubber is good for a DD, but there are better options out there, depending on how much you want to spend.
As utmorpheus implied, it's obviously good to have some sort of focus in mind if you do mod your car. To my mind, we already have one of the best cars to drive in the class, and I wanted to make mine look sharp while also making it more civilized with various gadgets and accessories that other cars in the class have (the '2 is a bit basic, but it is a lot lighter than a Fiesta or many others in the subcompact segment).
