One of the complaints I've had with all the previous versions of the game is how the AI routinely violates my border.   Why not implement a mechanism like almost all other strategy games have where the other nations/factions/etc must either ask for open borders treaty or declare war.   

Also, there should probably be some repercussion to other civs when my influence completely takes over their stations - without a open borders treaty.   If they are going to be foolish enough to build a space station near my territory it should be their loss if it later becomes completely under my control.

The late game is a bit of a slog once you get pretty far ahead and for me I got tired of slowly competing with another Civ for prestige.  I just decided to end it by going to war and wiping them off the map.  Also, a couple of the "Challenges"  seemed impossible as I was exploring anomalies with 5 ships for about 50 turns and still not uncovering either of the quest items