I put a mechanical fuel pressure gauge on my '93 with the RD2-110; hooked to the stock vacuum sensor spot(aka right after the fuel filter/separator).
I'm pushing about 4.5 PSI at idle, and about 3 at WOT. It's remarkably consistent, within 1 psi. This, to me, is perfect - consistent fuel pressure is key for consistent timing.
Mind you, this is pushing 250 RWHP, more than any stock IP can put out.
Yes, you could do some boost referenced fuel pressure stuff... if you want to mess with the timing. Add more psi = more advanced timing, to a point. It might be useful, if your IP isn't tuned right, or able to be tuned for good timing at full throttle. Otherwise, it's just going to screw things up.
I'd probably only play with that on an experimental rig - take the inlet transfer pump out of the IP, and just control the fuel pressure "manually". Mind you, this pressure would need to be up to 150 psi, which would take a pretty beefy pump.