The car is a fine motor - very reliable and solid engines. The GT Turbo has more upgrade options though - the non turbo is not often modified.
The best route would be an engine swap for the Turbo engine initially and then go for a larger turbo.
With your current engine :- Other things you can do is get the head flowed and skimmed, fit high compression pistons (unless you are still going to go the turbo route) Adding Nitrous also gives more power. Uprating the fuelling and bigger injectors will also release more power.