I play mostly on tiny/rare. I've made some additional observations:
- Turning off "cultural victory" seems to double your score. You then get a military victory by flipping all the AI planets. Similarly, turn off "tech victory" so you can get credit for reasearching each tech, but also the "military victory" bonus. Notice that military victory gets the highest multiplier. When you're about to win, gift planets to the suviving AI so you can get that last trade good and wonder.
- Play evil. Evil races get more trade goods and wonders, and you get a bonus for each trade good and wonder you produce.
- Have a few successful invasions. This seems to boost the military component of your score.
- Have a high average approval rating. This seems to factor into your score, in addition to the population points.
- Have a high average net income. This boosts the economy portion of your score. Trade starbases help here.