Congrats on your purchase! Do you have the Turbo or no? If not, there's still a tuner or two floating around who might be able to get you some low-end torque without sacrificing MPGs, but regardless of turbo, there isn't too much you can do to get a lot of gains out of this car.
If it's a turbo put premium in it for an extra 23hp over regular fuel.
I don't bother. Torque is rated the same premium or regular and it's what gets you going for the most part. Not worth the extra $ for me, but give it a go if you feel you need a bit extra higher RPM passing power.