I invested in it more for the timing issue than anything. Running proper timing and proper fuel reduces end-gas, and thusly reducing exhaust gas temperatures. This means your exhaust valves/ports/manifold/turbo all remain cooler, meaning more power.
I don't know why this isnt a more common thought among tuners, but less heat always means more power. It is concievable that you could make 400 horsepower out of your setup with the twist of a screw, but removing the heat from that 400 horsepower is what all the other modifications are about. You will run a larger intercooler, precise timing and fuel, and perfectly honed plumbing all for the sake of heat reduction (be it eliminating end-gas, stopping lean conditions, preventing headloss and turbulence, or decreasing the heat/compression ratio of your system).
Think about it, by controling when the burn starts, you can actually change your AFR by burning the mixture more completely. The heat benifits from this, namely beingable to squeeze under a lower preignition threshold (i.e. pump gas) while running higher effective compression, are keys that will turn your "10psi" into a lot more than the other guy's "10 psi".
With anything else, you leave the ignition tables as they were from the factory. You now depend on the durability of your components to perform well beyond their specifications. Japaneese automobiles have been known to be over-engineered, but were not designed anywhere near the conditions they will have to endure. Here in tuner-land, we call that reliability. In my honest opinion, you would enjoy your vehicle more if you believed in your tuning more than you relied on the engineering of your 10+ year old engine.