I like the idea of having different victory conditions depending on the final tournament score. As an example, I have thought that to control a planet you need to adjust its "loyalty" to your side. If all planets start at 0 points, and you gain a number of points equal to the difference of the final score (in an 8-3 win, you would gain 5 points). Once you have 10 points you gain control of the system. You would only gain "loyalty" points if you are attacking the system or have a round in which the system is not attacked. You can lose points when defending the system. Once you have control of the system, you gain the economy bonus and any special bonuses as well.