i've put a dump valve on mine and it has made no difference to the running of it at all. mines the 150 and it sounds awesome but i fitted one to a 130 and it didn't sound as good and i can only assume it's to do with the intercooler and the way the dumpvalve mounts on the car. if you're gonna do it make sure you get a bailey dual piston valve as they sound better. best way to get them to work is with a micro switch mounted on the throttle pedal via a specially made bracket which i can get hold of and wiring it to an actuator which acts as a valve letting the dump valve dump when you let off the throttle. as you may know, diesels don't run their own vacuum system so you need to splice into the brake vacuum but don't be alarmed about that as it still maintains the pressure, it's just to hold the dump valve shut. i certainly wouldn't rule out putting one on.
