once you have your 350bhp, you soon see what other parts need to be upgraded to cope
To be honest, I would agree with this. Whats the point of putting on mountain climbing boots to climb a hill unless you know you need them? How many people actually properly get the good of all the components they buy? I know I threw cash at my last car, and I am really not convinced some of the components were worth doing - specifically the Anti Roll Bars and Anti Lift Kit.
Having said that, I would probably look at component longevity over anything else if working within a budget. Higher power and torque will move the engine around severely and cause more severe wheel hop which will break downpipes, damage driveshafts, see the flywheel bang itself a lot inside the gearbox and do other suspension/drivetrain components no good. In addition, standard shocks and springs will see the car lean around enough to cause more traction/braking issues. Hence my thoughts on engine mounts and springs/shocks upgrades.
If you want to to track work, then look at anti roll bars, LSD's, uprated brakes, anti lift kits etc etc.