First - I just wanted to say thanks, Tony, and Gile.
As for identifying which Document has been registered using a bool Property is one of the samples I first found when lookin into all of this. I'll revisit that.
As for using LayoutSwitched && SystemVariableChanged; this will not function properly in MDI, as when one Document is in ModelSpace, and a second is in Layout with PViewport Active, switching between them does not change a Document level System Variable. Not sure if LayoutSwitched will fire, as I have not tested.
Hence my original need for both the DocumentCreated event (to register), and the DocumentActivated event (to evaluate the current space, or reconcile)... Each performed a different function.
Further adding to the mix, as I am attempting to enhance my VL routine, is that I have just learned that not even .NET API has direct exposure to the Preferences Objects, and must use COM first before accessing PreferencesDisplay, etc.
Not a big deal on the surface, but I am again disappointed to learn that I cannot simply monitor a Preferences*Modified event. If I am correct in my understanding, then even my .NET adaptation suffers similar limitations for accounting for user changes via Options dialog or VL functions which change Preferences* Objects outside of this plug-in.
** Edit to add - I know that I could simply monitor the Options CommandEnded && CommandWillStart, and all Lisp* event(s), but I guess I feel that I shouldn't have to. Such a critical object (such as preferences) should have a means by which to monitor changes. Am I just oblivious to a known method for doing this?
I'm going to have to give this more thought moving forward. Thank you again, for all of your assistance and feedback.