Now in CIV4TechInfos.xml:
Special techs
Are the following tech needed? They all have a <bDisable>1</bDisable> and miss many other tags.
TECH_SPECIAL_PROMOTION (appears as a prerequisite for a number of promotions, why?)
TECH_COLD_FUSION (appears as a prerequisite for PROMOTION_FUSION_CANNON and obsoletes BUILDING_NUCLEAR_POWERCOMPLEX in Atompunk)
TECH_RELIGION (doesn't seem used anywhere)
TECH_GLOBAL_GOVERNANCE (doesn't seem used anywhere)
<Help>
TECH_COOKED_FOOD is the only one with something defined here.
<iAdvancedStartCost>
TECH_MOUNTAINEERING has 125 here (vs. 100 for every other tech)
<iAIWeight>
It seems only used for a few mostly prehistorical techs:
TECH_RITUALISM|25
TECH_COUNTING|25
TECH_STONE_BUILDING|10
TECH_MEGALITH_CONSTRUCTION|10
TECH_SEDENTARY_LIFESTYLE|100
TECH_RESURRECTION|25
TECH_WRITING|100
TECH_KARMA|25
TECH_REINCARNATION|25
TECH_MACHINERY|100
TECH_PAVED_ROADS|100
TECH_FLINTLOCK|45
TECH_RIFLING|10
I guess that's understandable that the AI should have an increased focus on SedLifestyle or Writing (though why no other important tech like Tribalism or Trading?), but why the others (especially with low values such as 10 or 25)?
<iAITradeModifier>
I guess this tag increases the perceived value of the AI for tech trading; many important techs have 10, other have 0 and only one tech stands out with a 5, TECH_WATER_SPORTS.
<FirstFreeUnitClass>
TECH_GRAIN_GATHERING has UNITCLASS_GATHERER here - that's why the first one to get Gathering has a second free Gatherer and that every civ knows about it through a yellow message... I'd say this could be removed...
<bIrrigation>
Two techs are granting it, TECH_IRRIGATION and TECH_WATERWORKS, I guess there should only be one?
<bWaterWork>
Four techs are granting it, TECH_TRAP_FISHING, TECH_SPEARFISHING, TECH_BOAT_BUILDING, TECH_FISHING. I guess the first one would be sufficient since it's a prerequisite tech for the others...
<DomainType>
I think I remember a discussion some time ago about (too much) naval movement in the late game; if needed, here's the list of tech that increase naval movement by 1:
TECH_WEATHER_LORE
TECH_COMPASS
TECH_ASTROLABE
TECH_NAVIGATION
TECH_NAVAL_TACTICS
TECH_SEXTANT
TECH_SCREW_PROPELLER
TECH_REFRIGERATION
TECH_SONAR
<TerrainTrades>
There was a discussion about that in the C2C discussion thread. It seems both TECH_RAFT_BUILDING and TECH_SAILING unlock trade on coasts. Whichever is chosen (even another one), the excess ones should be removed.
<SoundMP>
What is this tag used for? Many techs have the same thing here as in <Sound>, while the others have nothing at all.
Unused tags:
<iAdvancedStartCostIncrease>
<bMapCentering>
<CommerceModifiers>
<iInflationModifier>