There's no automatic way to turn daily entries into a coherent whole. That is going to take effort by the author, and possibly quite a lot of effort; including rewriting to join essays together.
Using a "Best-of" tag is too coarse a division, unless the blog is laser-focused on only one topic.
I broach the subject with fear and trembling, because "new feature" is equivalent to "lots of new bugs and instability."
But... There are some things that would make connecting essays easier.
For example, suppose there was an option to order the presentation of essay in a category by rank. The most useful ranking is the author's (unless readership is static a Facebook-like "like" won't reflect real reader approval). The author then can put essays in some category in a "read this before that" order, deprecate things he changed his mind on, and so forth. Ranking in one category doesn't reflect ranking in other categories. This changes the "tag" structure associated with posts, but shouldn't be too hard to implement.
Simplicio: "But can't we do the same thing with meta-posts that consist of links to the others?"
Salviati: "Yes, but it is taxing for the reader to be perpetually jumping back and forth rather than reading longer blocks of related prose. In addition, it compels the author to edit old posts. Granted, there can be more connective detail between the links with the special-post format, but I think the user-interface argument is compelling.
Another thing that could make the user's experience easier is a way to use multiple tags in a single search: "Tribes" and "Geeks" for example. That requires a change in the generic user interface.
And one more thing: you create a structure consisting of different posts without bothering with tags, and tag the whole structure as a "book." A "book" might even include posts from other blogs, provided the authors of that blog all agreed to the inclusion (revocable at any time) and the outside posts were clearly formatted.
And if posts had version control available to the author and the reader--a "book"s version of a post could leave out duplicate introductory material (but still available for other views of the post).
Organizing the material is still going to be hard work.