The original wiki has questions, back-and-forth-discussion and loosely structured content on many pages. Maybe some pages need to be maintained/wikified/deprecated, but the EmacsWiki itself is fine. Also, it was never intended to be the authoritative GNU Emacs wiki. GNU Emacs is self-documenting. The non-standard stuff needs the wiki more.
Sure, if you're extremely comfortable reading emacs lisp spread across many files.
Just like Spanish doesn't need a dictionary, since it's self-defining once you move to Spain, and spend three months learning it via the total immersion method.
That said, the other 2/3 of the time Emacs does relatively well at self-documenting.
(Actually, my friends told me.)
I have always been frustrated by "traditional" wikis that intersperse random bits of discussion with the article. No one really seems to know where to discuss something. The threading is horrible.
I am very glad that Wikipedia realized that you need to separate discussion about an article from a single, authoritative, neutral article. They are two very different needs, and trying to mix them into one just doesn't work.
And for things like c2, I'd consider the lack of threading an advantage. For lots of technical discussions, this leads to clarifications that are hidden somewhere deep in that thread pile and would require an editor to factor those out in the main article. Which works fine with something that has a huge user base or paid people to work on it (i.e. Wikipedia or corp "wikis"), but not for everything.