A question being excellent does not make it on-topic, just like a question being on-topic does not make it a good question.
There are LOTS of very good questions that one could make about the common culture shared by us Spanish speakers: our openness, our traditions, our "touchy-ness", our take on family... and as much as I love talking about those topics, they are not appropriate for the Spanish Language stack.
Even when culture and language meet, the question can be still off-topic.
Has grammatical gender distinction found in the Spanish language effected or influenced in any way the patriarchal structures of gendered relations found in Spanish and Latin American communities?
A very good question indeed, but still not a question about the Spanish language. You can just assume that "Spanish language has gender distinction" and proceed to build up an answer based on Psychology, Social Science, Demography, Gender Studies and comparisons with other, non Spanish-speaking societies, without ever delving into Spanish grammar or structure or evolution.
Spanish language has a place in that equation, yes; but it is a constant, not a variable.
Now, to the question on point:
- It was about the culture of Spanish-speaking countries, not about the language itself. Op themself said so in their opening sentence:
This is more of a culture question [...]. So it was off-topic.
- On top of that, it was highly subjective.
May I go up to strangers to practice Spanish? Well, how the heck would I know? Everybody is different! Some people might like you talking them, some people might not. Some people might punch you in the face — and I'm not joking. So, opinion-based.
- Your edit to include the "how" only made it worse. Not only didn't it make the question on-topic, but it also opened up the opinion spectrum: some people might like you talking to them BUT not about the weather, some people might not like it BUT if you talk about soccer you'll be BFFs, some might disagree that you should not talk to drunk people... So, still off-topic and still opinion-based and now also too-broad.
- And speaking of drunk people... Just have a look at your answer. It could serve as an IPS template response about how to approach unknown people! You could just substitute German for Spanish and it would fit exactly as well. You could even drop every mention of language and the few example sentences, and it would still be a rather good answer to the question "How do I approach new people?". The answer being only tangential to Spanish is one of the most clear signs that the question itself was not on-topic to begin with. So, definitely off-topic.
About your edit, I'd like to mention that I don't think changing the scope of a question without the author's consent is OK.
As high-rep users, we have the privilege of editing posts without being subject to others' approval; and of course, it is good that we put that privilege to work to make questions and answers better. That doesn't mean we should unilaterally change the questions we don't like; by doing so, we risk striding too far from what OP intended to ask.
It is definitely OK to guide new users on their quest for on-topic-ness, making comments about what is wrong and what could be right, and even helping them with the edits once they've made their choice clear. And if their choice is to stick to the original, off-topic question, then the question should be closed. We can always ask a different, related on-topic question ourselves if we think it is a good question for the site. Hijacking another users's question to do so is not OK, in my opinion.
Finally, to answer your question:
Can this question be rescued?
No. The question was inherently off-topic, because the answer it sought pertained to the world of interpersonal relations, not to the world of Spanish language learning.
A question like "What are some common greetings in Spanish" would have probably been on-topic. But OP didn't want to learn some common greetings; if anything, they wanted to know if it was OK to approach new people to practice those greetings.
The only way to salvage the question would be to turn it into a different question, and it's OP's decision only to do so. If they don't want to change the question, then all we can do is close it, and make a new one ourselves.
