[God Emperor]

I think the tone acts as a modifier to how an AI considers a proposal. In the Politics.txt file, each race has a modifier for Pleading and Demanding. Some races give you a bonus for pleading, whilst others give you a penalty. I havent studied it in detail though to see whether the feature actually works.

With respect to races accepting treaties etc. From my observations, your score position and whether the AI is already at war seem to make alot of difference.

ie in some games a particular race has been very reluctant to do anything whilst in other games they are quite cooperative. The only difference seems to have been the factors I have mentioned.