Boost valves work on the return to tank fuel line. What they do is raise the pressure so that more fuel is ready to go into the cylinders, sorry I mean the fuel is at a higher pressure and you dont have to wait to increase fuel input via the injectors. A non boosted system has a very slight lag because fuel is allowed to return to the tank.
I have one on my other car and its true it does make it more responsive, but no extra power.