I would like to suggest creating different goals for a match, instead of having only the option to set “get X percent of stars”.
For example, in an old game that I played that resembles NP2, there was the “The Doomsday Machine” scenario, where starting from a circular galaxy the goal was to stay N turns in a star located exactly in the center of the galaxy, to be able to learn how to activate the Doomsday Machine that is located on this star system. Once a player learns that, he automatically wins.
Needless to say that the battles in the center of the galaxy were brutal.