imo,
The car is so capable with standard power that the best mod I've done is uprating the brakes. It can stop so much later than before.
If your really after the feeling of a quicker car then weight saving is the least expensive. Rear seats out, light weight front seats and your there without being to hardcore about it. BHP/ton is the best figure to look at instead of peak power.
You gain very little for a lot of money with these engine,I've got matched inlets and the R3/V6 airbox and although peak power comes in earlier and holds flat roughly 800rpm it cost a new slim battery for under the seat, wiring the battery and the airbox set-up.