Well, I haven't given up, but I still haven't found the cause of the rough idle.
Last night I did the following:
1) swapped the coil packs - no change.
2) Swapped the MAF sensor - no change.
3) Plugged the vacuum hoses connected to the fuel vapor canister (because I can hear the solenoid rattling sometimes) - no change.
4) Checked the wires and plugs again - all wires look ok and measure between 4k Ohms and 7.5 KOhms. All plugs were grayish white and the electrode wear looked normal but I regapped them to .060" again anyway - no change.
Since none of the plugs look to be oild fouled, or otherwise damaged, it doesn't seem logical that one injector could cause a lean condition for all cylinders.
So it still seems as if there'* a vacuum leak somewhere or maybe it'* a fuel pump/fuel pressure regulator porblem...
'99 Bonneville SLE, white, 112,000 miles
'02 Park Avenue Ultra, white diamond pearl, 88,000 miles