"Even if they weren't, pulling the fire switches during the evac. checklist depressurizes hydraulics so the flaps remain where they were left. "
Are
all fire handles pulled during an evac, Wastegate? If the APU was kept running, the main engine fire handles would have only stopped pressure coming from the engine-driven hydraulic pumps. In this case, you still could have extended the flaps using pnuematic/electric power from the APU (which would have been started up when the aircraft turned off the runway) or, failing that, by electrics from the Ground Power Unit (if it had already been plugged in at the gate). Extending flaps with vehicles/personnel around would have probably been more hazardous, however.
"By comparison, on the 767, the inboard spoilers auto - retract when the overwing exits are opened, so I recall !!"
Correct. However, the 747-400 inboard spoilers appear to be well outboard of the off-wing slide (see pic below). In any case, the spoilers should have been down at the gate.
http://members.ozemail.com.au/~b744er/KALtail2.jpg
Regards.
Q.