slotted/drilled rotors make the car have less stopping power, Caleb.
The decreased surface area means less contact with the pad, and thus more stopping ditance.
However, over long, hard, repeated stops, these slots/drills will allow the gasses to escape from under the pad, lessening the affect of brake fade.
On a Celica, unless you autox, the upgraded rotors are just for looks.
What you need on your 2004 GT are some decent pads/shoes.
buy a new set of rotors ($44 is worth not having rust) and some good pads. TRD
, EBC, Hawk.
As for the shoes, not many companies make high Performance shoes, but you can do better than OEM.