First of all: by setting the date to before 1989 wont make any difference...or does the WTC reappear when flying before 9/11??
Not necessarily, but the World Trade Center appears in my Flight Simulator world via an add-on scenery package. There were certain parameters to make it visible, and once I managed to make Flight Simulator meet those parameters, I saved several flights in my FS "Saved Flights" folder to allow me to fly in Manhattan in a pre- September 11, 2001 -era.
Does this make me any less of a person in doing so? Absolutely not. For one, I have a personal connection by way of one of my uncles who's an Ironworker. He and his Ironworkers Union helped rebuild the underground superstructure beneath the World Trade Center Hotel after the February 1993 attack, and has shown me several dozen photos he took while he stayed in Manhattan doing the rebuilding work.
That, and I have a very deep appreciation for their design and how they were built.
As for the Berlin Wall, it may be a matter of taste. I know for a fact that in Flight Simulator 98, any flight after November or December 1989 does not show the Berlin Wall. Any flight beforehand, however, shows the Berlin Wall.