- I made massive edits to the accepted answer
No, you didn't. You tweaked the code formatting and added a couple more examples. The spirit and meaning of the answer is alive and well.
II. I deleted 8+ "duplicate" answers in that question, including a 17 upvote and 13 upvote answer in that question.
This is tricky... I hate duplicate answers. I've been known to downvote every answer to a question save one, purely because they added nothing to that one. Even if that one answer preceded them by seconds... Because, really, who wants that noise?
As The jjnguy is fond of pointing out, different wording for the same thing can be useful. Some folks just need a little different wording to understand what's being shown them. So the fact that there are 18 answers to that question isn't necessarily a bad thing...
Except that a pile of them are duplicates. Exact duplicates. And in two years, no one downvoted them, no one commented on them, and no one improved them... They just sat there, repeating what the accepted answer already said, taking up space. I'm not sure why you deleted the answer that opted to describe the syntax for CASE instead of giving concrete examples; it may not have been all that great of an answer for most folks, but it did give the answer in a different way. But that still leaves at least 5 answers that add nothing.
Anyway... The specifics:
- Should there be any answer deletion? No answer deletion? Some answer deletion?
My personal preference is that authors delete their own answers when they fail to add anything new. Commenting and downvoting is a reasonable way to encourage this...
Failing that, I advocate a conservative approach: leave them alone until they're doing actual harm. What harm can a duplicate answer do? In this case, obscuring the new answers, specifically: one that was inapplicable (but not downvoted) and one that correctly noted the existence of a new method (previously suggested, but inapplicable at the time).
- Should we play favorites improving the top voted answer / first answer?
Yes! If you do that, who cares how many other answers there are? It sucks to be the guy not getting any rep for noticing that
IIF now exists, but it's great to be the next reader who doesn't have to troll through 18 answers to find it!
- Will deleting answers with +17 and +13 score turn away high rep users?
It is impossible to predict and a shame no one bothered pointing out that they were duplicates two years ago though...
- Has this asset become a public resource, whatever that means?
Well, yes. The asker got his answer two, almost *three years ago. The 160K readers since are the only reason it's worth keeping around, and the core reason for having this site in the first place!
- What should we do when new answers trickle in and are dupes?
Downvote them, perhaps leave a comment noting that this answer already exists and that they should try to add something new if they really must bother. Protect the question if useful. Delete once the noise level injures the ability of future readers to evaluate new and novel answers.