RD-BH
Human
...
Currency IMO is the most important tech in the game. I highly value it. The sooner I get Alpha the sooner I get Currency. There are many times I build research on top of building wealth.
...
And why do spies have nothing to do with passive espionage. Do you not use spy siege?
Currency is researched:
... after Mathematics (250x

... ... increases chop yield.
... ... unlocks Aqueduct (+2


... ... unlocks Fort (various uses)
... ... unlocks Hanging Gardens (w/Aqueduct)
-or-
... after Alphabet (300x

... ... build Research
... ... unlocks Spies
... ... Tech Trading (if enabled)
... ... Tech Brokering (if enabled)
I do on occasion use spy siege,
... but more often use promoted mounts and/or advanced melee.
By the time I'm starting to build Wealth,
... I'm usually >20x

... 100x

... I have the option to quick build Hanging Gardens. (situational)
... Workers can build Forts. (situational: canals/resources/defence/stack muster)
Alphabet loses [some of its] usefullness because of where it is in the Tech tree.