Here and there, I see answers prefaced by "this is really just a comment that got too long" or the like (and after seeing this a few times I felt comfortable doing it myself, twice in fact). Is that acceptable, or does the fact that it might crowd out the real answers make it very bad? Does it make a difference if the extended comment-answer is also helpful in getting to an answer?
From our Help Center's page on "How do I write a good answer?":
Answer the question
Read the question carefully. What, specifically, is the question asking for? Make sure your answer provides that – or a viable alternative. The answer can be “don’t do that”, but it should also include “try this instead”. Any answer that gets the asker going in the right direction is helpful, but do try to mention any limitations, assumptions or simplifications in your answer. Brevity is acceptable, but fuller explanations are better.
Standard Stack Exchange doctrine is that answers need to at least provide information that could be helpful toward getting an answer to the question, preferably explicitly stating how they do so. I don't see any reason why Mi Yodeya should hew to a different standard.
Applying this standard to examples that were brought up in comments to this question:
The question this answer was posted on stipulated to the existence of the "ng" pronunciation in the past and asked if people had heard it in use in the present. So, additional evidence that it has been used in the past will not, presumably, lead to an answer and therefore does not constitute an answer. [Some of] it might be valuable as additions, perhaps in footnotes, to the question post.
The final line of the answer:
"FWIW, I've also heard older community members pronounce Hebrew this way."
does directly address the question, though vaguely. The addition of more information about the location and/or backgrounds of said community members could make it much more valuable.
This answer provides rulings related to the issue in the question that could well suggest approaches to that issue, so I would say that it does constitute an answer. It could be improved a great deal with the addition of explicit analysis of how the cited rulings may relate to the question at hand.
For what its worth, I checked out those two examples and saw that I had already up-voted those two specific non-answers a few days ago.
I think that if you acknowledge that it is not an actual answer, but you are still bringing valuable material, then you should post it. Over the long haul, it is better for everyone if valuable material gets posted, even if it might not fit the formal definition of an answer. I would have confidence in the voting and accepting system that users on average will give more votes to real answers than to interesting ancillary material. That occurred in these two examples, at least.
People might say that it could dilute the quality of the question-answer format, but I think that happens only when the material has little value (rants, jokes, smart-alack remarks). I have posted those occasionally and subsequently deleted them after realizing their inappropriateness. The difference between that crap and what you are providing is that your "extensive comments" do have inherent value.