OK, problem solved (I think). I found 2 broken wires in the harness leading into the driver's door, which explained why the driver's outside power mirror didn't work, and why the master door lock button wouldn't lock, only unlock, the doors. While in there, I double checked and re-cleaned the trunk switch/button, and checked the wire for continuity to the harness plug. All good.
I then held the door button down and pushed the glove box button out (off) and in again (on). I noticed that as long as the glove box button was held in tight with finger pressure, the door button worked every time, but it would fail if the glove box button was just set to the 'on' position. So I removed the glove box switch, disassembled it and bent the 2 contact lugs slightly upward. The design of this switch relies on the slight spring pressure of the button assembly contact bar on both of these lugs, not a great way to go IMO.
If this had failed to fix the problem, I'd just put in a jumper to permenantly allow the door button to always trip the trunk lid. I know the intent is to push the switch off and lock the glovebox to prevent the valet from getting into the trunk. Myself, the last time I experienced valet parking was on a holiday in Miami 30 years ago.
Oh, one last note....I got a Compustar remote (1WAMR-1600) with the car, but it didn't work to pop the trunk. After hours of searching, I finally found the installation manual for the remote ECU (CM5200), which also had a nice wiring pin-out label right on it. I scrounged up a tiny pin connector out of an old VCR and connected it to the wire from the door switch, which now allows me to use the remote to pop the trunk. Woo-Hoo