Seeing as how the point has come up.
The first settle is tempered by the fear that someone may call trade, drop a windfall, and be off to the races. It's a real tension. (This reminds me of the poisoned craftsman in Puerto Rico). I'm not sure if there's a hard and fast rule.
If you don't have a consume power (and a windfall of your own), then it's less of a problem. You may give up a trade, but you'll get one later on. (Of course, the tempo means that you won't be out of cards). Sparta can settle, but may be better off just exploring to get a few more military cards. The issue there is that Sparta really doesn't want to let those pesky developers get a head start.
Alpha Centauri and Earth's Lost Colony have less incentive to settle, since they can trade/produce without helping anyone else. (ELC is, admittedly, less likely to do this).
Epsilon Eridini (and, amusingly, Earth's Lost Colony) don't necessarily mind getting a poor windfall consume. Eridini gets a card (and a VP), but saves a tempo. ELC gets a VP but can then produce and trade for a bonus VP.
Looking at this from a Game Theoretic point of view, I suspect that you just have to toss a bit of effective randomness in. You don't have to actually be random ... you can use information only you know ... like the cards in your hand.
But if we took a situation where we knew all the cards (say, set hands, but changing them around so that there were windfalls aplenty) then I think the optimal play would be Settle X%, Trade Y% Other Z%. Early on the Trade play will be surprising, and work fairly often. Then people will become suspicious and the Settle % will fall. This will, in turn, make the Trade % plummet. Which allows the Settle % to rise.
So ... no real answers.
Thoughts:
- I'm more likely to settle if I can pick a windfall (if no trade hits) or a nice production world (if it does). And if I've got the matching "produce on a windfall" card, I'll almost certainly do it.
- If my developments are poor, then part of me wants to explore (to get a good one), but that still leaves reasonable odds of coming up empty and seeing only developments.
- Earth's Lost Colony can always produce, for a mini-trade (less upside, but less downside).