This is just how I'd tweak things.

Terrans- keep the same.  I can't see any addition that would work

Arceans- keep the same.

Torians- keep the same

Yor- their super ability effect should scale with the amount of engine tech they research, and should be a "movement point" cost instead of a flat out limit.  Should be 1 at start, 2 when impulse is acquired, 3 when warp is acquired, 4 when hyperwarp is acquired.

Drengin- amount of corvettes they get should scale to planet populations.  Type of corvettes they get should scale to economic wealth of planet.  They can build the best corvette they can under a cost related to the bc received by the planet

Altarians- if the human refuses the altarians request for aid, they suffer a morale penalty.

Korx- keep the same.

Drath- maybe tweak its effectiveness to be less, and allow Drath to offer humans something to attack others.

Iconians- change their tech tree to where their Extreme Colonization tech gives 25% colonization all words.  (untrade/stealable)  Their SA is they get this tech turn 1 insteaad of having to reasearch it.

Thalans- keep the same

Korath- make the korath research advanced toxic worlds before getting the spore ship?

Krynn- keep the same