For this question, I ended up leaving three comments (one on the question and two on different answers). Some content might be reasonably edited into an answer (e.g., replacing "moonless" with "starless") since it would not substantially change the sense of the original writing, but other content would require what would almost be a rewrite of the answer (which seems rude--even though reverting is not difficult). On the other hand, providing an answer that merely rephrases another answer with one small improvement in content also seems somewhat rude and probably discourages the best answer from rising to the top (because readers might see the improved answer as excessively derivative and not upvote it and the writer of the earlier answer might be hesitant to incorporate the improvement).
So the question: When should content be included in a comment (possibly like a footnote with alternative content or possibly with the hope that the original writer will incorporate any worthy content or be inspired to leapfrog even that improvement), an edit, or a separate answer?
Even though I am more tempted than average to leave "substantial" comments, others seem also to be tempted to "answer" in a comment (because the "answer" is perceived as too incomplete to be a "real answer", because it is really more an addition to an existing answer, because comments have low risk [not just reputation but perceived sense of authority]). Therefore, I think some guidelines might be helpful.
The particular example is probably not a good one for evaluating the problem. With a little extra effort all three comments could be merged (with some additional content) into a decent--I am rather proud of the contents of the comments--answer.