I think there is a case to post independent questions in separate posts even if the questions are related. I’m not advocating the forceful splitting of a question in two against the asker’s will, but just a general recommendation.
In particular in the case of the two questions mentioned in the original post, I think there is no harm in splitting them in two, and there are potential benefits.
Earthling discusses in another answer two potential benefits from having two related questions, namely about the etymology of two synonyms, together in one question. I think those potential benefits are real but need not be lost if the question is split in two.
Viewers interested in one question will likely be interested in the other one too. That is quite likely, but we can simply cross-reference the two questions. For instance, “word X and word Y both mean such and such. This other question [link] deals with the etymology of word X; here we are concerned with word Y…”
If you answer one question you may have something useful to say about the other one. In this case you can simply post two answers; or one answer to one question and a comment to the other if you think you don’t have enough for a proper answer to it.
Accepting an answer is simpler. We sometimes get two good answers and don’t know which one to accept. With two questions in one this problem is magnified: one answer may give a good account of the etymology of word X and a poor one of word Y, and another answer do the opposite. With two separate questions you simply accept the two good answers.
Viewers can focus on one issue at a time. When there are several answers to one question I like to compare them. Especially when I don’t know much about the subject and cannot properly evaluate or even fully understand an answer, reading them all helps. Generally when the subject is complex or there is a lot of information one needs time to reflect on things; sometimes one wants to go back and forth between answers. It’s easier to do that if each answer is really just one answer rather than two answers one after the other.
Answers will be shorter. Some people, or even most people some of the time, baulk at the prospect of reading a very long answer. Having two answers one after the other compounds the problem. If we have two separate threads instead we can read one now and come back later for the other.
Viewers will feel more encouraged to answer. If we have two questions in one, viewers may hesitate to take on the research to answer them both. Or if they feel they can answer one of the questions but don’t feel confident about the other they may hesitate to post an answer to one of the questions only. We will likely get more answers if the questions are posted separately.
There will be more posts in all. Given the low traffic in our community this is in itself an advantage.
I’m not suggesting we artificially multiply questions. I’m talking about questions like the two examples in the original post: we actually have two different questions in each of them. I have now posted an answer to the xuxinha-and-rabicó question dealing with xuxinha only. If I managed to write and post an ok answer to the rabicó part, wich I don’t think I can, then it really would be two answers, one after the other, in the same post.
To reiterate, I’m not suggesting one should compel askers to split related questions into separate posts. But we could have this as a recommendation. Say, when someone posts two related questions in one, and it looks like the related questions will generate independent answers, we could leave a comment suggesting that it may be advantageous to post the questions separately and, say, direct the asker to this thread.