... past the point where you expanded beyond a decent number of systems?
From what I read in several AARs, mostly VB6 admittedly, people quit before losing, or quit when starting to lose (because VB6 was slow...), or quit because bored expanding.
Now, the AI in C# Aurora is better, so I wonder if it can really go to the throat and conquer your home system, if you manage to expand significantly. I have no doubt it can go for the kill if you are still in the early phase of the game, but a common problem of AIs in strategy games is their difficulty finishing a player once established with a decent power base.
Additional question: did you ever had to go into exile from your home system, planning for your vengeance against a NPR