Here is my suggestion
Training:
Miners: Source of TBG, gets X gold for Dwarves, Orcs, and Elves, and (X+25%) gold for Humans.
X is the unknown amount of turn based gold per soldier, It would have to be higher than the current TBG per soldier, because the fact that you have to pay for miners, making the TBG a LOT smaller than it is currently.
These miners of course would cost gold to train.
Trained Attack soldiers: Orcs get 50% TBG For trained attack soldiers,
all other race recieve no gold.
Trained Defence soldiers: Dwarves Get 50% TBG for trained defence soldiers, all other races recieve no gold.
Spies: Elves get 50% TBG for spies, all other races recieve no gold.
Humans gain 5%-10% for trained attack, trained defence, and spies
Humans gain 25% TBG for untrained soldiers.
Other races gain 15% TBG for untrained soldiers
I know people have been complaining about Human's disadvantages, but, currently, I am being Dwarf, and i see that we dwarves are the worst race (Even Mav agreed with me). So, Dwarves should get 25% more DA and 10% more Sentry.
Most Dwarves want to be a DA wh0re, but when elves Gold Recon them, the entire strategy is demolished.
Orcs could get 10% more spy rating to balance out the Dwarve's stat increase.
Adding in the Sentry stat would also decrease the elvish advantage, (They get Attack power of GR, and defence power of Defending from GR and recons). With Sentry, Elves can be gold reconned in return

.
Humans would have a bigger advantage with the untrained soldier TBG bonus.
Dwarves could defend from attacks better.
Elves would no longer be the superior race.
I know people with think that Elves at a large disadvantage, but remember, you have an entirely different way of attacking which is harder for other races to defend.