This query raises an interesting dichotomy between conservation best practices and interpretive integrity. I believe that the maps in question were issued primarily, if not exclusively, to pilots and air crews to assist in escape and evasion if they should be forced to bail out or make an emergency landing in hostile territory. They were carried, neatly folded, in flight suit pockets or in the crowns of flight helmets. The ones I’ve seen were folded so neatly and uniformly that I suspect they were originally issued in that folded state. (There must be WWII vets still living who could verify or refute this.)
To the extent that this is true, the removal of fold creases, even though it may be appropriate from a conservation perspective and may yield a more aesthetically attractive artifact, actually transforms the object into something that it was never intended to be in its original use context.
At the very least, if unfolding and de-creasing is deemed necessary and appropriate for the sake of preservation, the original folded/creased condition should be photographically documented, and that documentary image should be incorporated into any interpretive display.