drengin get -25 to diplomacy but korath don't?

I've noticed this as well, when you choose your opponents you can see their + and -. And on Drengin and Korath it says - diplomacy so both should recieve a negative modifier, yet only Drengin recieves it as you pointed out. My bet is that they forgot to change it and it will be patched.

Spore weapons count as diplomatic advantage.

There is also Iconians which have +100% Espionage with no bonus to research when i assumed that Iconians is the Technologist race

Strange, isn't Krynn supposed to be the spy? If I remember correct they only got +50% Espionage.

I think that now the +/- also reflect the races tech trees. Korath have -diplomacy as they have very few or no techs which increase diplomancy.

If you also notice, a lot of the negatives a race has are countered, and then bettered by an early tech they have. Examples: Altarians have -10% weapons, but they get Dark Energy Lab pretty easily which gives them +30% weapons. Arceans are -1spd, but they get Navigation Centers, etc.. Look at the total package.

Personally, I think it looks like there has been, from the release of DA on, an effort to balance the game such that the Korath are stronger than the Drengin. They get a much better super ability, better starting bonuses and now a better tech tree. This looks quite deliberate. My guess is that the story requires the Korath to be stronger than the standard Drenging they sprang from. I actually don't mind the weakness of the Drengin relative to the Korath, because otherwise they may play pretty indentically.

One other note: The starting +1 speed the Drengin get is actually pretty useful, and balances out the diplomacy penalty, and they've got the best ground troops in the game (excluding the Arceans choosing to build 45 or more cathedrals of valor).

Speed is life. Its no coincidence that it costs 5 pts as a special ability.

iconians aren't meant to be a tech race, they've got tons of arnor technology but they barely understand most of it.