You mention a dump valve. If this is for the TDI140 in your profile then you'll be wasting your money.
If you've had an air filter and a remap, then I'd suggest for the moment that you save your money on the go faster stuff and concentrate on putting that power on the road. Suspension upgrades will
help with roadholding and ride comfort, and don't forget that whipping along faster means that you have to stop aswell. Decent tires will keep you on the road instead of in the ditch, and if the brakes are getting down then consider some better pads & discs maybe.
My personal favourite is a dose of Millers diesel plus in every tank. An added benefit of this is that you don't need to declare it to your insurers, unlike the remap and air filter upgrade you have.