OK... Nothing good to report but I do know more...
First, thanks for the flow chart. I did see that last night when reviewing the 'Further Reading' link you posted and finding the 'Jandy Troubleshooting Manual...' but having it here was quicker.
Disconnected the SPA control panel and tested - No change.
Confirmed that 9.96 volts is available at pins 1&4 at the control box and at the panel location. Also confirmed continuity for pins 2&3/wires 2&3. (Actually, that line is quite nice solid core ~20g wire so pretty tough)
Also tried connecting the remote panel with a short set of leads. Nada... The panel does not do anything but illuminate the amber power indicator.
Correct me if I am wrong but even if the comms chip / PCB are bad, when first powering up, wouldn't the remote panel at least display some sort of initial local boot messages or wouldn't the LCD screen or backlight at least illuminate?
That screen does nothing at all so presuming at least one of those are true then that remote panel must be dead as a doornail...
Here are some pics of the inside:
View attachment 629259 View attachment 629260 View attachment 629261
View attachment 629263
Not sure what it means in the scheme of things yet but based on the dip switches, I gather this is an "older AquaLink board as it does not have the second set of dip switches.
This is what I have:
View attachment 629265
Now... How to proceed...
I still feel like the issue is the control panel(s) and not the comms PCB but perhaps it is both (bummer).
I did not check the voltage on pins 2&3 but even if I do, would that really confirm the comms PCB is working?
If my quick search is correct, replacing the OneTouch panel will be about $600.
I'm not sure if I'm reading it right but I might have a 'L' revision PCB so pretty old. It sort of seems I would need the iQ30-RS kit to move to iAqualink for about $1,200? Money aside, would that be a better solution? It seems more flexible as I gather it can be accessed from iPhone / Android or any HTML5 browser but I do like the idea of just a simple wall mounted panel - guess I could get a cheap Android tablet and mount that to the wall 
More to the point, would going with that upgrade remove all the known issues I currently have, meaning that would replace the comms chip(s) and give me a working control UI?
Thanks very much for the guidance !!!