After playing Sioux in countless treaty 20 FFAs and actually winning some games, and losing to other FFA treaty Sioux players, here's my recommendations:
Treaty 10-20: No changes needed. 20 mins sees you booming into a FI with 70-90 vills and a huge pop army and your DS button will give you a quorum of dog soldiers at this point. You still have hunts on the map, can send more bison than Carter has liver pills, and the only resource you need that isn't protected or by your TC is mining.
Treaty 30+: This is where most people have a problem. The Sioux are not balanced for this length of treaty or longer. The biggest problem is lack of coin. Walls are important too, but if you can afford to build a large offensive force, the walls become less important because you take the fight to their base.
One suggestion I had was for the wood/coin trickle card to self-upgrade at the 10-minute and 20-minute mark. Start out at its current low level, then increase slightly after every 10 minutes of gameplay until 30 minutes when the trickle rate = European wood trickle + European coin trickle. If the card is sent later in the game, have the trickle rate auto-adjust to the actual game time, not start out at the lowest rate. People would tend to not abuse this as Sioux because they are naturally balanced for rushing and not for stalling.
Another suggestion would be to increase or improve the infinite native allies or mercenary allies shipment. Instead of a large number of mediocre outlaws, send quality allies like elite or champion native dorks of some sort.
Thirdly a shipment like Colonial Militia that give you an option besides 1500 food for 10 dog soldiers at the tc. This would be good for both treaty and non-treaty alike. Double Warriors or something that come out instantly, even if your dancers are garrisoned.
As for other ideas ITT I think they have beat the wakina cost issue to death and settled on the current cost indefinitely. DS train speed is a little slow I agree, I don't see this budging anytime soon.
Clubmen/cetans: You have better options late game and find yourself using a lot less wood anyways, so changing this for treaty would be sorta pointless.
Infi hunts would be nice but more important is the coin issue. A plantation card is hard to justify given the flavor of the civ, but I still would use it if it existed.
Crunkatog on ESO
Bart331 balance suggestion: aztec: remove civ
Voltiguer: Ender, Sioux in 1.04 will be a top civ, no matter how many layers of Sioux goggles you put on
schildpad on Elephants: ...their mansabdar unit sucks so hard it looks like a black hole
Crunkatog on Steam.