When I got my first 2x3 Graphic, a 2x3 Pacemaker Speed Graphic, its ground glass was very dirty. Cleaning helped, replacing the GG with a SatinSnow GG (made by Dave Parker, no longer in business, alas) helped more. I use one of Dave's GGs on my Century Graphic too. My 2x3 Cambos (yes, plural) have their original ground glasses. They're fine. I've used a variety of loupes, primarily Ednalite Magnifinders and now a 3.6x Toyo.
A Cambo in-line viewing hood (2x3 size, SF-320) is very useful. I have a 2x3 Horseman monocular reflex finder. I don't like it, too dim, but usable.
I also shoot 2x3 with a 4x5 Cambo SC. The original issue Cambo GG is just fine. I recently replaced it with a Boscreen (spelling?), am still not sure it gives better results.
Practically speaking none of my 2x3 cameras has a usable rangefinder. I have no choice, must focus on the GG, don't feel deprived.
Zone focus? You might as well shoot a 35 mm rangefinder or SLR and get the plane of best focus where you want it. More seriously, Crumpet, you're much too locked into the 35mm/digital imitation 35 mm mindset. The typical 2x3 and 4x5 camera doesn't have focusing scales (one needed for each lens) and it doesn't have lenses in focusing mounts either.