performance parts > looks
and that's not necessarily go-fast parts. you can easily get performance parts while helping the looks too. spring/shocks/coilovers will make your car look better while giving you better handling. exhaust will make your car look meaner while giving you slightly more power.
personally, i rather go for performance parts. i've probably spent $76 on looks. that includes $75 for my lip and $1 for the red tape to mask my spoiler holes :P
like brian said, "No one wants a car that looks good, and gets passed by grandma in her Caddy." and if you do, then that's the original definition of a ricer