It's sort of the Avengers Endgame of the 80s Star Trek novels--a number of characters from other novels get cameos or namechecks. Chris Claremont does the same sort of thing in Debt of Honor. Both stories involve a Big Crisis and a crew of lots of guest stars from the past are assembled for this mission. (There's no link in Debt of Honor to the 80s novels, though ISTR one minor character is named after Diane Duane.)
It's funny you put it that way; that's much the way I viewed it going in, and what I wanted and hope for. I read it know it as a focal point for many of the novels that I assembled for reading. It had an additional, somewhat erroneous significance, having to do with the coming of TNG. I tried to pin down which book was the "final" novel of this sequence, the last TOS novel released before Star Trek started to broaden. Somehow I incorrectly landed on Time for Yesterday as the marker for right before TNG's arrival.
I figured it would help to be aware of that transitional moment. I had a view of finishing the book as the beginning of the end for the idea of a "Star Trek 80's novel continuity" as a concept. My list still has something like 9 novels past that point that I thought of as kind of a death blow to the idea...nine additional books is a pretty respectable "victory lap" if it can be called that. (To say nothing of the books that I've skipped/saved for rainy days, such as Chain of Attack, Uhura's Song, and the ones I read decades before my current readthrough).
And I read Memory Prime thinking of it as partly of a new era. It didn't let me down, felt loaded with references to the previous books on the list...and one sneaky little reference/nod to the Tkon from TNG's "The Last Outpost". I had mixed feelings about that moment.
To circle back to the idea of Time for Yesterday as a finale, I read it in that way. It's impressive how it manages to be epic in scope, as well as very focused on individual characters on a relatable level. As a finale, I think the major missing element was not having Ingrit Tomson as the security chief. Imagine her leading the other returning security characters from Vonda McIntyre's novels, with her habitual gall, she would have been the perfect character to beam down and interrupt Spock from being naughty!
I was struck by Time for Yesterday as kind of it's own story, though, I ended up feeling like maybe I wouldn't have needed to read all the previous books as a lead in...if I were in the right frame of mind. I think I might be kidding myself though, the little continuity nods might have driven me crazy, wondering what I was missing! I was glad to be in the know, with just a little regret that I hadn't tackled Uhura's Song and Tears of the Singers before going in.