If you hit a culture ruin AND build Monument second, then opening Tradition before going into Liberty isn't a bad idea. The Liberty settler shouldn't come too early anyway, as you might not yet have luxes online. Trad-Lib mix is > Lib in many situations, I think. But my view on Petra is that it's only worth building if there all of the following 3 are true:
- It's still available as a Liberty finisher (obv.)
- There is a really good spot for it
- You didn't plan for it, so haven't compromised tech
Even then, scientist, or using the Engineer for another wonder, might well be better.
Agreed about Trad-Lib mix > Lib.
Agreed that it needs to be available (duh
) and needs a good spot to justify.
As for planning for it, I've usually semi-committed to it when I decide to open Liberty. This isn't a full commitment, as I can just go left side of Liberty and then go back to Tradition very easily, but I'm calculating my odds at this point (and trying to get a glimpse of every other Capital looking for desert). The decision point is when I skip the free settler and go to right side of Liberty. I can think of no other time where I would do this diversion (assumes I have stolen my workers).
Regarding tech compromise: I'm usually beelining Philosophy anyways and building Oracle while waiting for libraries to finish in expos. Grabbing the three techs to get Currency isn't much of a diversion. It may slow down reaching Uni's by 8-10 turns, but that's not really a concern for me. Early science is very important. Mid-game, not so much, as I generally make my big move in tech late game anyways. Perhaps this is why I don't finish with sub-250 times, but (to bring up a longstanding discussion) optimizing finishing time isn't the same as optimizing the likelihood of winning.
Not using the Liberty finisher on a GS can somewhat be made up for by the fact that you got early Oracle, which will give you a relatively early GS anyways (especially if you get garden and National Epic in Capital early).
Saving the GE for another wonder can be forced on you if someone grabs Petra right before you, and that's fine. You're going to have some great options, and this is just about the only scenario where I find myself getting LToP. However, with a good Petra location, it's one of the most powerful Wonders in the game.
One thing I didn't mention is that taking a cultural pantheon makes a huge difference in this gambit. I might consider just beelining Currency in this scenario, but that's an entirely different strategy altogether.
At the end of the day, DON'T hard build Petra, IMHO (exceptions apply). The opportunity cost of losing out on it is too great.