Have you considered tweaking how the promotion system works out fried? If you examine the way people promote their units in mp games, it seems that a minority of players understand the powerfulness of how to properly upgrade units a myriad of ways down to an art. The majority of players seem to upgrade units as more of an afterthought.
Some of the promotions do not seem to make sense in my opinion, such as Guerrilla and Woodsman I/II. When you think of elite, specific environment trained forces of today, and throughout history, most applied such traits towards attack. Defending in this game is ridiculously easy, especially when a player has their roads up and an adequate number of catapults to back up a defense force. If a defender camps his units in his territory in a defensive tile (forest, hill, forest/hill) with a road on it plus the appropriate terrain promotion, it can make them nearly impossible to kill as they can catapult you before you get near a city and mounted vs. the appropriate defensive unit of the era in such a situation favours the defender even more ie. Horse Archer/Knight nearly any melee vs. Longbow with Guerrilla on a hill = death to the attacker.
There is already a defending promotion....City Defender
I believe the Guerrilla and Woodsman promotions should be applied as a bonus in an opposite way, in such that the attacker negates that specific, defensive terrain feature. When I think of the US Army Rangers, they attack especially well in wooded situations, the 10th Mountain Division, 10th Special Forces Group specialize in Mountain warfare, the Finnish military during the Winter War vs. the Soviets....these units utilized their strengths in attacking. I believe the trade-off is fair and does not unbalance combat as players have to sacrifice a general strength upgrade (the Combat series of promotions) or an anti-unit specific upgrade (Shock, Formation, Pinch, etc) on a unit. It will reduce the need in mp games for the "..." stack sized militaries that needlessly lengthen games, gives players in certain choked situations an easier time in removing an early choke (especially in ancient) if you have a barracks as the battle you'll be now fighting is closer to a 50/50 chance of winning rather than a 25% chance or less of winning.
I still believe that Guerrilla/Woodsman II should give the double movement through the applicable terrain, but should not give the defensive bonuses as I pointed out above. My prime example for why this change should be implemented is in Medieval/Renaissance starts you start out with an explorer. Explorers are notoriously difficult to kill in these eras, more so in Medieval than in Renaissance. I had 2 Explorers and 2 archers fight off 3 impressively sized stacks in a forest/hill outside an opponent's city. I don't remember the exact make-up, but you can ask Pipman as he has nightmares about this still.
The Samurai UU...I don't understand why it seems this unit gets a penalty towards its production vs. that of other UUs. The hammer count is the same as the macemen, but the resources it requires to build is limited to iron, rather than a choice of iron or copper. No other unit seems to be penalized in such a fashion. Some units can be built in the absence of the resources needed to build the non-UU version it replaces, ie. Jaguar and Camel Archer. It came as a shock to me when it was pointed out to me that Samurai needed iron and copper could not build Samurai. I believe that the Samurai UU is otherwise balanced as they can stand toe to toe with Knights when properly upgraded and still pack a punch on the defensive vs. Cavalry with the 1-2 first strikes. They can more than stand up to any other melee unit with the appropriate upgrades on defense and can wreak havoc again if you have the appropriate upgrades. I think Samurai are one of the most under-rated UUs in the game.
As for India....maybe think about giving them something other than an elephant unit as elephants are powerful enough. Perhaps give them a rifleman based unit like the Gurkha.
The Cossack does have ridiculous stats in comparison to other UUs vs. their regular counterparts. However, Cossacks are defeatable by cavalry with the Flanking II promotions and a little help from catapults. With the loss of a catapult, 3 Cavalry with Flanking II will take out 2 Cossacks with Combat II most of the time. It seems that 60% withdrawal rate is overlooked on cavalry with such promotions, it's priceless watching a stack of Cavalry devastate a stack of Cossacks and have over half your cavalry withdraw. So you sacrifice a few catapults....they're the peons of Civ IV.
The movement issue....once again, I'll hearken toward the need to revamp Guerrilla/Woodsman upgrades. I believe the change will encourage players to use those upgrades more, if you're upgrading to attack with those, the next logical step is to apply the 2nd such promotion that'll give you that double movement if you want to get there faster. I believe it's a good trade-off. You sacrifice more combat power for mobility which has been the problem with militaries traditionally. You either move fast and hit light, but hope you hit in a soft spot that multiplies your attack. Or you move slow but hit like a sledgehammer.
The only people I really see taking issue with the proposed changes to the promotion system I recommend are the single player gamers out there. However, the AI is pretty weak as it is, so hopefully this encourages them to play multi-player. Multi-player is the future of gaming, unless you have AI that is as strong as the AI in the Galactic Civilization games put out by Stardock.....down with cheating AIs.
I did not realize this was a ladder mod....I thought this was something that would hopefully be applied to future patches. Not sure who I should send these proposals to as the Civ IV official website only redirects you to Take2 representatives. There does not seem to be an official Civ IV forum....very odd....considering most games this big have official forums where these concerns can be voiced.