They're getting close to this. Hindered slightly by the fact that much of the historical information contained in the archives has changed recently, sometimes in major ways, sometimes in subtle ways. It does appear that recent work is polishing lots of the rougher edges, which will encourage more people to try, which should increase the volume of information shared here about it.
To some degree, the ease of list manipulation with Lisp-like languages is a double edged sword. On the one hand, it's very powerful to manipulate things in raw form this way; no need to construct a bunch of abstract data types, and APIs, for manipulating data structures! Very very flexible. However, over time the representation changes, and things that worked no longer work exactly the same. Each individual ends up recreating his/her own "toolbox".
A project of this sort will probably never reach a point where the "api" or "coding style" or "best practice of manipulating the data structures" is frozen for good. But there is a kind of "style" of approaching problems, in a known constructive way, that good books can sometimes teach.
I agree it would be outdated by the time it was written, in terms of API/data structure coverage. But some set of documents might be able to better encapsulate the "way of working". I see the evolution of this kind of guidance in the scheme-hacking documentation that's part of 2.17.x.
Same here.