Revamp diplomacy. The economy, the resources, the private market ships and their logic all seem very tight to me and work very well.
The diplomacy between the star empires should be modified, more options for talking and trading, etc.
But first, start with implementing SUBJUGATION properly and make a race's (or several species) victory condition a set percentage of total empires.
Subjugation should result in an empire giving you 10-20% total income, all their ships/planets known, a sizeable research bonus to your empire, and when you declare war on someone the subjugated race MUST declare war as your ally with you. When you put trade sanctions on them, they do the same. Also, when you wish for them to make peace with another race, they obey (of course, they cannot start wars on their own).
However, a subjugated race's number one goal is to get out of subjugation. To that end, they will work tirelessly to get secret-allies who will pledge to help them get out of subjugation. Once a military parity or superiority between the subjugated empire and their allies (who can be other subjugated empires of the same evil race!) happens, then a revolt takes place which means a war between an evil overlord empire and its subjugated race(s) and its allies.
To further work this concept, some goody-goody empire's race winning conditions can have a number of subjugated empire's liberated to add to their victory points total.
THIS BETTER HAPPEN.
< Message edited by Timotheus -- 12/15/2013 11:24:31 PM >