Want to thank everybody for their comments, both in general and specifically about my posts here. They have made me sit down and think about my negative 'gut reaction' to Fantasy in Historical 4X games.
I still firmly believe that complete Fantasy (Orcs or Elves hopping around the map) has no place in a Historical game.
On the other hand, there are a lot of fantasy/'unreal' elements that were Firmly Believed by people living in historical eras, and it seems, on reflection, not historical to leave out some representation of the beliefs. After all, people's Actions were influenced by those beliefs, and often to the point of having real historical relevance.
For instance, and they have been the subject of discussions in other Threads: Astrology or Alchemy as 'Techs'. They are usually described, at best, as 'pseudo-sciences' rather than 'real' technologies/sciences, BUT they were both immensely influential in the development of Astronomy, Mathematics, Chemistry and Physics. In fact, recent scholarship suggests that the Primary motivation for early Astronomical studies, calculations and observations was for Astrological reasons. So, without Astrology, Astronomy and Mathematics might be delayed considerably.
Likewise, the Mythologies of the world that include Vampires, Werewolves, Elves, Trolls, Magic Mountains, Fountains of Youth, Eldorado, Shangri La, Mordor, etc. were (and are!) very real to very many people. IF the game purports to show 'historical' actions and reactions, it is going to have to deal with actions and reactions to mythology and fantasy as well.
BUT, I'm still going to draw a line: No Vampires or Trolls or Soothsayers wandering the map. Instead, (in my Perfect Historical 4X Game - which I suppose is another Mythological Creature) the game should reflect the effect that people's Belief in Vampires or Soothsayers had on their historical actions.
As, for instance, the use that Vlad Tepes made of people's belief in Vampires to establish a reputation so fearsome that even the prospect of fighting against him made enemy leaders reconsider. Or the effort expended by various Europeans hunting for El Dorado or the Fountain of Youth or Prestor John.
It is, perhaps, too subtle a difference for many, and certainly doesn't provide the instant commercial appeal of playing a game that includes Vampires or lightning-throwing Apostles, but it can include an Army or Leader that are associated with Vampires and thus produce negative modifiers to their enemies, or a Prophecy by a Soothsayer (or Oracle, to bring it down to historical earth) that affects decision-making in a State, Leader or group.
And while the Fountain of Youth might be nothing more than a spring of unpolluted water that keeps your men healthy, the Search for the Fountain might lead you to discover Florida or Oklahoma - which may represent a random Effect, since, as in most such Searches, the end result is not what you started out looking for . . .