I have a 51 Bugeye WRX which has a full Hayward and Scott turbo back decat (sounds goooood ), free flow filter upgraded intercooler y piece uprated fuel pump and a Andy Forrest remap (all done before I got the car), Andy Forrest reckoned it was about 280bhp/280 torque when it was mapped. It drives and pulls really well.
To be honest I would start with brakes and handling mods first if I was starting from scratch..........but I am an old man!! That said I am looking at upgrading my turbo soon