I’m not insisting that any senryu must be grammatically correct or complete. Eye of the beholder and all that. Please continue to interpret them as you prefer.
These aren’t haiku, though, they are mostly lightweight comedic observations and closer to jokes than high art — they definitely aren’t intended to be imponderable (they’re intended as entertainment for wide audiences and are mostly contest submissions).
I interpret this one as meaning
“If you ask them about their traditional dance hobby, it’s bon-odori”
Putting it into 3 stanzas (ignoring syllable counts), the poem form does become something closer to your “independent” version:
“traditional dance” hobby?
if you ask
it’s bon-odori
I think most Japanese natives would interpret it this way (though they might substitute me/my for them/their).
I think humans are wired to express complete thoughts most of the time. Your three “independent thought” English interpretation still uses punctuation to express a unifying thought rather than complete independence. It could even be diagrammed even as a grammatical English sentence if you begin the third stanza with “It’s the” (see below for my thoughts on the incompleteness of “noun phrases” in the two languages).
I also interpret your English version quite similar to what I diagrammed (I get a strong sense of “is” coupling between Macarena and hobby/dance). My only quibble is that I think 趣味日舞 is constructed as a compound noun. I think it literally means “traditional-Japanese-dance-hobby” — the word “for” in your first stanza seems to detract from the connection between the last stanza and the first.
Grammar/diagramming thoughts
We should probably continue this in the diagramming thread if you wish to reply to my thoughts in this section.
A “noun phrase” being something ungrammatical/incomplete? I really don’t think that’s the case in Japanese.
The single word 雨 (rain) would sound complete and grammatical in Japanese conversation (after 「なんの音？」or 「なんで行かない？」perhaps), but often wouldn’t in English (it would sound like you were muttering to yourself if you just said “rain” – you’d be sore tempted to say “it’s raining” or something similar).
[Probably not the best example.]
I think implying だ is even more common in senryu than in everyday conversation because of 音数 constraints.
In English it would absolutely require a verb to be complete and grammatical: “Rain falls” perhaps. Making it an object would requires two additional words, the verb “is” and a pronoun for the subject: “It is rain”.
But in Japanese subjects are omitted constantly. And predicates are pretty much universally seen as the most important part of a Japanese sentence. At least I’m convinced that if all you have is a single noun, it belongs in the predicate.
If it’s not the subject then you pretty much have to assume an implied だ。
I disagree. A bareword noun in Japanese absolutely says that noun “is something”. It doesn’t simply exist, nor does it do anything: it is something else (unspecified but implied by context, exactly what the zero pronoun is for).
「綺麗な花」
「面白い冗談」
Both strongly imply a final だ but it wouldn’t be unusual at all to leave it off in casual conversation (or in poems!).
This was my mistake back during the nose-ring poem: I initially interpreted the bare-word noun as a subject and wrote 「鼻ピアスがある」(causing many to throw up all over my diagram 
). But interpreting it as a subject has a problem: what verb do you assume? Depending on context, the subject 鼻ピアス could be followed by 落ちている、忘れた、見つからない… It wouldn’t be simply ある in some contexts.
But if you assume 鼻ピアス is in the predicate, then だ always works (because of the zero pronoun as the subject).
I don’t follow why that’s a concern. In the English sentence “If you want to know the weather, it’s raining” the independent clause “it’s raining” will also be true regardless of the desire.
)
) In other words, it can be interpreted only as “[Time] with [any boyfriend]” the way it is written.