What tyres are you running? did you check the pressures before you went out on track? did you check them when you came back in?
When you changed the suspension bushes did you change the Steering rack ones?
Have you had your alignment checked?
Green Stuff are ok for fast road use (although to be fair I'm going back a while since I used a set in anger). Brother in law has some in his Z4 and they seem to do the job well enough last time I had a play in it. Not sure they are quite up to snuff for prolonged track abuse as they do the Red Stuff for that.
What ever you do a pretty standard S12 is never going to hold it's own against Caterhams, Lotus' and such in the bends, got to compare eggs with eggs. That said leaving them behind in a straight line in no mean feat either!
It's not the worst handling car in the world but I do know what you mean about feeling a little disconnected from the drive, unfortunately that is probably more down to the compromises made to keep the day to day driving more pleasant....... and it's some 20 years old!
Pound for pound the best "performance" mod you can ever make is to get some proper tuition. It stays with you no matter what car you jump in and helps you understand what you can change to make the car better. Someone told me once that unless their can lap within 2 10ths of the same lap time everytime, then they always look at the organic matter between the seat and the steering wheel before changing any car setup parameters. That's a bit extreme for trackday fun but the theory is sound. You'll get more enjoyment out of learning to drive a car better than having to constantly change things/spend money on it to make up for driving shortfalls.
Hope some of that makes sense and you didn't nod off before the end
