If you don't have a adjustable reg then there isno need to have one on the car. Its a good good idea to check your pressure at least with a hand held gauge to make sure your pump and reg are up to specs
39 psi with vacuum off. With vacuum on it should rise up a few psi under load.
Only reason i would have one on a car without a reg is to see if you were running out of fuel at the end of a run. I had a detonation problem at the end of my 1/4 mile run. After watching the fuel pressure drop off 5psi towards the end of 3rd gear i discovered my fuel pump was crapping out on me.
I would recommend one... I had problems all last year with my fuel system b/c my fuel pump was not holding enough pressure... It was at 20 lbs and it needs to be at 38-40 at idle and around 45-47 under throttle for 24 lb injectors...It would have solved my probelm befor eit even happened if i would have had a fuel pressure gauge. I am putting one in my new stang