The Best of Trek books were some of my earliest exposures to the idea of fandom at large. (
The Best of Trek #13 was also one of the first Trek-related books I ever owned.) I liked reading the sort of speculation I could find in there, because I hardly ever had the chance to discuss those things with anyone else...
...which is basically the reason I don't think such a series would work particularly well today. The Internet has made it possible for me (or anyone else) to delve into whatever fandom they want as much as they want to, including the ability to contribute with a very short turnaround time, all of which basically serves the same function as these books (and the zine whence their articles came) were serving.
Even at the time, I found a lot of the material very dated--the articles
barely started covering material like TNG and
Star Trek V before the anthologies ended. (I kept waiting for the analyses of
Star Trek VI which never came.
) Some of the earliest collections are from a time before TMP, filled with longing for "Gene" to bring TOS back, and I think a lot of it would be interesting to read now from a historical perspective, but I can have a lot of the discussions I was looking for in there much more quickly and effectively online.
At the same time, there was some stuff that I liked, even if I agree with
KRAD that the in-depth articles were few and far between. I liked the listing of minor
Enterprise crewmembers from the novels and episodes, the speculative chronologies for the mainstream universe and the Mirror Universe (whose point of divergence was actually Khan winning the Eugenics Wars, though the
Challenger explosion was mentioned, IIRC), the breakdown of Klingon culture and
klingonaase from the novels up to that point, and various articles which tried to creatively extrapolate from the limited material of TOS, TAS, and the few first movies to explain what was inconsistent or merely absent from the canon.
That sort of work reminded me of the games Sherlockians play with their canon, and it's something I already do automatically when it comes to things like timelines, so I liked "playing along" with someone's train of thought in an article. Sometimes, people seemed a little too fixated on particular topics (I don't really care
that much about how
pon farr would come about, from a biological perspective), but the concept yielded at least some results that I enjoyed.
What seems to be happening now, in terms of printed material that covers similar ground, is that such articles/essays are only published offline when there's somewhat more editorial control and/or access over the finished product. The trend in books is towards more scholarly collections of essays (I'm thinking of titles like
Enterprise Zones or
Finding Serenity here), while the licenced magazines benefit from having articles written by the tie-in writers and others more closely associated with the source material.
But I can brush it off. 
