You're not going to experience any more performance with the IC or the tower brace. The IC will help your engine last longer and help prevent heat soak. It's more preventative than additional. There are many upgrades that claim more HP but that is contingent on help from other mods. A tune is your first and best bang for the buck.
There's no bottleneck with the ST's intake, exhaust, turbos and intercooler under stock conditions. All those stock parts will flow more HP as is. It's the ECU programming that keeps the power back. That's why a tune is your first line of modification for more oomph. It opens up the possibility of adding more power.
That is all mostly true, and I'm already aware.
Honestly, the heatsoak and easing breathing was reason enough for me to do the upgrades. (Adding a tune in the future and unleashing tons of performance gives future benefits)
Can the OEM parts run at its current HP levels and above?
Of course - it is the same for most powertrains.
The thing is that
inefficient parts of the powertrain create parasitic HP/Tq losses, and inhibits performance of the engine at some points in the RPM range, etc.
Obviously, when you tune the engine's performance by changing the tune, you get "the most" benefit, so I wouldnt expect a lot, but there is a change.
As for changing the strut tower bar - HP doesnt influence its uaage nearly as much as hard driving/track days