Regarding the wiring diagram, while I believe that this is a good idea, and I recall seeing one for a 1985+ Pearson 30-something, I also think that it may be impractical.
Realize that wires are located in three dimensional space. A diagram only represents the location in two dimensions. How would you discern a wire running through the headliner from one running under the cabin soule? I guess that you could construct several diagrams showing "layers."
I have a hard liner, and don't have any wiring up there. The port and starboard wiring all runs under the gunwales, and any wiring down the middle runs under the cabin sole, so two dimensions would work. But your point is well taken. I'm playing around with Open Office Draw. It seems you can layer drawings. If so, you could have a separate layer for the wiring in the liner. I'll post what I come up with. I might even do a layer for lighting vs. mechanical (for example).
In addition to being an aid in diagnosis, I think the diagram would give an overall view that would be very helpful. I sometimes look at the way other people (including the manufacturer) did work and think "why did they do that?". Hell....I even look at my own work and wonder the same thing! I trace on my hands an knees for 15 minutes and suddenly have an Ah-Ha moment.
Having a overview would show the relationship between electrical components, and possibly more efficient ways to connect them.
In building construction we call it a "as built" plan. As opposed to a "as planned" plan. AKA...A reality check!