Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.
Please consider testing and adding an alternative end-game condition: a player has settled five planets. We've tinkered with it a tad in our group as it seemed to provide an option for someone behind in the upgrade race to make a run at ending the game quickly before the dice/ship advantage becomes overwhelming. I can't say we've played enough to be sure this is balanced, but it does seem to warrant further testing. Just a thought.
We also would love to see greater variance in the secret missions if you are trying to come up with stretch goals.