I did a bi-xenon conversion to my 05GT and it was a BIG TIME improvement. Got the kit from visionbulbs.com. Less than $200 for the H13 hi/low kit. Comes with dual ballasts, install is pretty simple, bulbs snap right in to the headlight housings. And I just passed inspection with them. They have a discount code you can use to get 10% (if I remember right) off the price and offer free standard shipping.
As for the exhaust, like everyone else has said, get a set of GT exhaust off of ebay.
Hawgman