I've been noodling through my earlier experiment with the dual batteries and the in-line fuse. I was incorrect to assume the trunk battery only ran the starter. It also powered the main relay (injectors) and the fuel pumps via the drive relay. This doesn't totally explain the it-worked-yesterday-but-not-today phenomenon, however. It does seem that cleaning the in line fuse did something.
Incidentally, my in-line fuse enters the ECU harness/connector and then there's a red wire from the ECU harness to the drive relay (pin 30). This is a little different than Papajam's schematic for a 1984 Spider that shows the in-line fuse directly to the drive relay. I'd like to know what that is about.