The wiki is out of date. I was pulling old numbers off. That only reiterates my point though; this UNW has gone through 3 rounds of nerfs, putting it at 1/5 the power of the base national wonder just to try to balance it.
More importantly, the White Tower needs to do something other than give +1 spy. Having 3 spies in Renaissance that act 25% faster while everyone else has 1 is the thing that launches England ahead. ignoring the lead in levels your spies have, that is still 3.75x the amount of spy actions for an entire era. Making the White tower's base building something other than the NIA releases the wonder from having to grant that third spy, and lets it stack with the NIA later, instead of giving a gimped NIA extremely early.
UNW - White Tower (replaces Ironworks):
available at Machinery
requires Forge
+10 for

Production, +2

Culture, +2

Science, +2

Gold
+3

City Defense
+2 Iron Resources
+3

Culture to all Castles and Constabularies on Empire
Contains 1

great work of art/artifact slot, which comes filled with the

Crown Jewels great work
25

Science for every building

Construction in this city, scaling with Era.
20

science and

gold when you perform an Advanced Action, steal a Great Work or Technology, complete a City-State coup or Election Rigging, or kill a foreign Spy in this City (+5

/

for Advanced Actions), all scaling with Era.
-1

from Distress in this City.