"I actually have a trip to Spain planned for next year!"
Excellent plan!
"That will be my first experience of a Spanish-speaking country".
If you can't hack it in Spain you sure as heck won't be able to hack it in Latin America. After your Spanish trip Latin America will be a lot lot easier for you to adapt to (less of a culture shock).
"Nonetheless, I really don't view any part of the European Union as a place I would consider living in"
You'll be able to make that judgement after your Spain trip. Southern (Mediterranean) Europe is a lot different from northern Europe.
"But I am interested in why you connect Spain and Portugal to LatAm. I didn't really think of them as all too culturally similar anymore, though there's obviously language, Catholicism, shared history, so yeah actually they are pretty obviously similar, but I was just coming from the idea that one is firmly part of the modern West, while the other appears to be more of its own civilizational sphere".
Spain has all the stuff that you'll see in Latin America (warm weather, beautiful churches, baroque architecture etc.) but it's a lot safer. It's not like a British person going to Australia which has the same British culture but the weather, architecture, general environment is totally different.
In the big cities of Latin America you will find all of the same things that you have in north America (Starbucks, McDonalds etc.) The big problem with Latin America is the violence problem. People from Latin America love Spain as the culture is so similar to the Latin culture minus the safety / security challenges. Spain is Latin America with training wheels.