[Q]

You propose to things that would generally be excellent additions to SE IV apart from the new treaty "cease fire":
1.) That actions between two players have an effect on all the other players attitude/mood against these players. Other examples where this might be very interesting is the use of certain weapons (star and planet destroyer, plague bombs) as has been proposed before.
2.) That the AI would be willing to end war against a certain gift/tribute.

I believe the "cease fire" could be equivalent to the already existing "non intercourse" if the latter was really meaningful (I never understood what was the real difference between no treaty and no intercourse treaty). If you have this treaty no ships will attack even if accidently (warp point) in the same sector, but ships can't enter the sector where the other empire is already present.