You will get no benefits at all from a second dump valve.

You may get some benefits from removing yours though, or better still put a resitrictor in the pipe that T's off for it so that although it works it only leaks a small amount of pressure, taht way the intercooler wont totally depressurise but it will still help protect the blades.

You are aware are you that if you remove all the resistance to the turbo by excessively large dump valves, that it can allow the turbo to overspin and go to fast which can lead to damage?