Mapping wise it depends who ask, been told that you can get up 290bhp/340ft lbs on just a re-map alone, most of the guys here (who have far more knowledge than I do) will be able to tell you more.
I had some suspension work done a couple of months back, sh!t load of bushes, sti front control arms, sti rear anti-roll bar, front anti-lift kit etc, gives you quite a lot of fed back through the wheel, had the back end try and break away from me when I had to jump on the brakes after having the work done and could feel exactly what the rear was trying to do, just still too much body roll for my liking so will look at the whiteline anti-roll bars at some point.
I bought a 2nd hand Kakimoto exhaust on wednesday from Jap Performance Parts in Crawley, not much louder than the Prodrive system, although going through a tunnel you can hear the differece
I'd say pop up there and have a look at what they have mate, your welcome to have a listen to mine sometime so you can judge for yourself.