It seems like we could consolidate much of the above discussion into a trichotomy:
Diplomats would form treaties and try to work together with other races. They would gain benefits to research, and trade from all of the interaction. This strategy would have the additional benefit of being able to get help in a pinch, but backstabbing is always a problem, and allies will often take up space that you could put to better use.
Isolationists would "turtle up" and focus on developing their own infrastructure to provide for themselves. They would have strong defenses and be resistant to espionage. This strategy could be the most versatile in terms of victory conditions because you can adapt your focus to serve the current situation (research vs production), but you would not have the available resources of other strategies.
Warriors would have highly trained units and good production, but would probably suffer in research. Warriors would have the best access to resources and would have the most population, but much of that will be needed to support the war machine, rather than develop for the future, so they would probably aim to win quickly. They would also have the most colonies and the weakest defense (due to rapid expansion), so a single, concentrated, counterstrike could cut supply lines and leave them helpless. Also a technologically superior fleet might be able to trump their superior numbers and experience.
I wonder if this would work as a rock-paper-scissors balance, or if it would depend too much on where you start, what you find, and how other players behave (or don't behave