The GT-As run a slightly smaller turbo which gives it a fatter midrange with less top end. It works really nicely with the auto and short-shifting second-third out of corners is an awesome feeling. They came with a wide variety of options (i.e Recaro front seats are optional, as is the regular Evo 7 rear wing) and a number of colours that were never available in the regular Evo 7s, so make sure you look carefully at what you're getting. It's fairly common to switch to the Evo 8 MR factory turbo (or even the normal Evo 7 turbo), as they can easily handle 22psi for daily use.
The tiptronic box, however, is prone to overheating, and replacing/repairing it is where the expense comes in. Basically, get a trans cooler if you plan to do any mods to the motor.