RESOLVED. See below.
I called Mitsubishi tech support and, with Mitsubishi Mark's help, have resolved this. Below are the steps I used to view device values in an offline PLC program.
I'm not sure that all steps below are necessary, or if there might be short cuts, but these are none-the-less the steps I used. Efficiency suggestions would be appreciated.
Connect to the PLC with GX Works2.
Menu: "Online>>Read from PLC..."
Click "Select All" button. (Probably only need to check the "Device Memory" check boxes in the "Module Data" area. But I clicked the "Select All" button; Mitsu newby attitude to cover myself.)
Click "Execute" button. If dialog boxes pup up, accept them all. When done, click the "Close" button.
Unplug from PLC, just to prove the point.
Double-click in Navigation pane Project>>Device Memory>>MAIN. A spreadsheet-like presentation is opened in a "Device Memory MAIN" tab in the main window. In the "Column Selection" dialog box that popped up, I accepted the "Auto" default and clicked "OK". A spreadsheet-like presentation is provided with values for the various devices.
At this point, we may want to select what particular device values we want to observe rather than scrolling through all the rows, and may want to change the format of the value display. Right-click the top-left cell of the spreadsheet-like presentation and click on "Input Device..."
For my use, I did: "Device: Y", "Range>>Address: 0 to 27", "Display Mode: BIN", "Register: 16-bit", then clicked the "OK" button.
Then, I added to the display by going through the "right-click>>Input Device..." again: "Device: D", "Range>>Address: 0 to 7", "Display Mode: Dec", "Register: 32-bit", then clicked the "OK" button.
I now have a display that shows the Y outputs and the D register values I want to observe at the top of the spreadsheet-like presentation.
Caveats: I do not know how quickly the device values are saved, so the complete device value set may be skewed in time. This would be best done with a PLC program that was not changing any values for the duration of the transfer of values from PLC to PC.