How to determine if printer/plotter is configured to plot a file, not to a device?
I don't think it can be. Even when you choose "Plot to File," the next time you call up Plot, that option is again unselected. When you pick on "Plot to File," it adds the words "(this plot only)". At least through A2004 -- it may be different in 2005. Kent Cooper, AIA ...
What you sad is true for single "re-direction"; but if you create a new printer and set it's output to a file, AutoCAD will select automatically the "Plot to File" option anytime you select that printer. However there should be a way of determining if a printer is configured to plot to a file not to a device.