I like my ST but it is just not the car for me. I crave hardcore performance and the ST is not that but a refined sporty compact just like the ST badge represents. It is an amazingly fun car but for it to be what I want it to be I would have to keep modding.
If the RS wasn't coming out this is what I would do.
EFR6258, I want that turbo to keep spooling up top but also do not want to dampen that great throttle response.
Wavetrac LSD, The ST really has trouble putting power down and can easily roast the inside tire especially with all that TQ and immediate throttle response.
I would upgrade the clutch at the same time, as for what I don't know. I havn't researched in over a year due to the RS. I will say I loved my Stage 3 KY clutch in my balt, but instead of Ceramic I would probably go Kevlar due to being more slip friendly around town, and I have a lot of hills. I use to have to dump the clutch on my Balt and spin the tires so I wouldn't annihilate the clutch up big hills.
AP Racing brakes
Again I haven't researched in a while but at the time the best damper system out there was the GC kit using Koni Yellows and Eibach springs, but I would really love a set of MCS dampers.
I would swap out all the bushings for stiffer ones.
A set of lightweight Forged Wheels.