People on the forum are a varied crowd hence these sorts of tactics will inevitably vary and also there will often be no across the board consensus on these. I resort to following journals and trying to see how trajectories align. For example, with @JollyScot I know that we have some commonalities in terms of spouse's place of origin and that we re both UK based; also earlier (in this journal I think) spoke about the trickiness of getting Spanish passport and then needing to verbally renounce UK nationality (even though in practice, it would still be a valid nationality in the eyes of the world outside Spain). So the comment about dealing with Spain using South American passport with the view of DW hypothetically applying for an EU (Spanish) passport down the road was in this context.
But this is hypothetical as at the moment we are happily based in the UK. Though it is becoming more of a possibility as DW works for a major Spanish company and will move there for work for 1/4 to 1/3 of this year.
In relation to building FI in Spain, whilst doing it from scratch is maybe not the smartest (I did the same search for FIRE blogs based in Spain @dara and found none, though my Spanish is poor), moving to Spain when already comfortable with money can be an adventure, as others mentioned there is more to it than money alone.
Also, I am trying to use proportionate response regarding money - either by intelligent design or by natural endowment. This is another way of saying that I personally struggle to aim for being a high earning and also having a lot of savings
We as a household thought are strong in low outgoings. And for this sort of lifestyle, Spain might be good.
Finally, the Spanish passport would be really a nice-to-have and an insurance for DW, since we as a household already hold one EU passport. But I imagine now if DW wants to apply for a random job in the EU, she would have to do some explaining along the lines of 'I have the right to work at your company based on the freedom of movement of family members of EU citizens' or something to this effect.