Right or wrong here is my opinion on the matter:
1) How can there be a spike on the pump from the hose if there is an unloader between the pump and the hose? The unloader stops the pressure from returning back to the pump head because of the check-valve on it's output.
2) I have customers that run 500 to 600 feet of hose with no problems eccept they loose 1 pound of pressure per foot of 3/8 hose. With a gauge on the pump there is no spike present to support the theorys that you guys are stating. A 400 psi deadband spike is normal for a lock-up unloader.
3) pulsation dampeners are normally used to remove pulsation on a coil to reduce wear and tear not to remove a spike. They are used to smooth out the water flow like a shock on a car makes the body have a smoothe ride. They also smothe out the flow of water so you can get an accurate reading on the pressure guage.
4) If you have a flow unloader the pressure will release as the flow thru the gun is on or off with very little spike.
5) The main reason for spikes are caused by improper unloader adjustment and wrong tip sizes. A properly adjusted unloader will release within one second of the release of the trigger. If you can count to 2 then your unloader is not adjusted properly and there lies your problem.
6) A hose acts as a natural spike/shock absorber, it expands and contracts as pressure is applied and released from your trigger gun. If you don't believe that look at the hose when you use the pressure washer. With that in mind imagine for a second the differencees in a short hose and a long hose. The short hose has less area to expand and collapse than a long hose so , with that in mind a long hose will dampen the spike way better than a short hose will. This is why the manufactures of paint sprayers always suggest using atleast a 50ft hose when using an airless paint sprayer. It puts out between 1500 and 3000 psi just like a pressure washer does.
You don't need to waste your money on something you already have designed into the system! The longer the hose the better the ability to absorb the spike.