I have no idea what a power boost valve is but on a NA engine it sounds like complete boll*cks to me. It could be like the WUR mod on a 1.8 16v engine but that runs k-jet injection so is really fundamentally different.
From what I can remember in other threads ABF remaps will get you about 3-5 bhp extra top end (not a lot of use unless you always change up at 7000rpm), a bit more throttle response and maybe a couple of bhp lower down the rev range if you're lucky.
As far as I know there's no easy gains to be had with these engines. If you want to go fast just try to always keep it above 4000rpm!
Losing some weight from the car is probably the quickest and easiest way of getting some extra speed. For a start never put more than 1/4 of a tank of petrol in...
