A new larger DLC should be focused on Diplomacy, Cultural and Trade. And in order to make these influences more valid War have to change.
Each war have to fill a purpose, these ever going wars between civilisations that can´t reach each others has to go. Is the war to curb the Drengin perhaps the reason for war is to decrease their military strength with 25 %. Perhaps a reason for war is to eliminate one cultural space station, when it is gone it should be way easier to make Peace. Et cetera.
This also means that raiding a border and attacking a ship should not be an automatic declaration of war. There are many reasons for a civilisation to not start a war because one ship gets shot down. There are several spy planes shot down during the Cold war but no side wanted to start hostilities.
Cold war has to be an option. You should be able to wage diplomatic, cultural and trade war agains your arch nemesis. But not military war. The trade war could be made through third persons. But also by using pirates. Remove the space psychopaths that are there now and exchange them with a modifier that hurts trade income per hex affected. Make it possible to divert fundings to enhance and create pirate areas in the enemy territory. To lessen the pirates you have to divert military fleets to the area who dampens the pirate modifier within their sector range. Only a fleet with an individual within it have the possibilty to find the secret hidden pirate base. To eliminate the pirate threat the pirate base has to be taken out.
Alliances needs one extra layer, the possibility to make an Alliance organisation (NATO, Warsaw pact). Being part of an Alliance organisation should meant that you have to divert some ships to them, but on the other hand so does all other members. These Alliance organisation fleets should be controlled by the leader of the organisation and have logistics +xx to make them something worth working for.
It should be possible to use the three influences to affect other civilisations choices. Make them become more hostile towards other civilisations, make them start wars you know the basic stuff. But also make it possible to use your influences to stop ongoing wars you are not involved in. If one of your smaller allies are involved in a war against some other weak civilisation you are trading with. You should be able to bring them to peace talks.
Your civilizations outlook as good , neutral or evil should be affected by diplomatic and trade choices. If you make a trade deal that is more profitable to the other side you become more good. If you use your military strenght to push other civilizations into bad trade deals you become more evil.