I've seen people reference these covers as simply generic book cover art that wasn't carefully researched by which ever artist did the cover at the time. There are all kinds of interesting curiosities going on with them.
One major part of these covers was how the uniforms and the ship didn't match. There would be covers with characters in their TV series uniforms of gold, blue, and red, and the Enterprise would be in refitted configuration (Dreams of a Raven, Chain of Attack, ect). I think I've seen a couple of books showing characters in their Motion Picture uniforms, but the Enterprise looks as she does in TOS.
There is something of an overall effect that I remember the covers having when I would look at them as a kid. Before a certain age, I had never seen The Motion Picture and never seen pictures of the uniforms from that movie, so I only knew of the TOS uniforms and the Wrath of Khan and beyond movie costumes. The book covers that showed TMP uniforms were fascinating, the first look I had at them; made me wonder about the time the book was set in.
The coloring inaccuracies were another interesting curiosity. There's a version of the Enterprise on the interior cover of The Final Frontier with features the Enterprise's deflector dish and nacelle tips as light blue (makes me think of discussions about the proper color when it comes to the 2009 movie). Then there's Yesterday's Son, featuring the top of Spock's maroon uniform style, except that it's more pastel colored, like TMP.
Accuracy issues aside, there's this foggy look to the artwork, which is really evocative, I think. Gives the picture a larger-than-life quality. Dwellers in the Crucible, The Final Reflection, The Wounded Sky and so many others, have this hazy quality that is haunting
. It's also a bit fantasy-ish, which, although I know Star Trek is generally more properly considered Science Fiction, the old show seems significantly less Hard Sci-Fi these days, with some of the concepts it explores and the way it does so.
A couple years ago, when I watched through the entirety of TOS on DVD, I bounced around between episodes, rather than watching them in the order they were arranged. Through something of a random quirk, I found myself watching a string of episodes that had a really hefty dose of swordplay, as well as some elements that on the surface appear magical (Trelane, swords appearing in Day of the Dove). It struck me that watching the right string of episodes and being none the wiser, a newcoming might regard Star Trek as something of a Sword and Planet series of adventures. And that's what some of those covers capture as well, IMO.
When I got to the point where I was familiar with the layout of Star Trek's internal history, it's progression from series through the movies, I would still read those books and be open minded about what my mind's eye would present. When I read Dreams of a Raven, even though I knew that I was supposed to set the story during the TV series, I still played with the images in my head. I pictured everyone in their TOS uniforms, just as the cover does, but the interior and exterior I pictured as a version of Enterprise from TWoK, and pictured the starship battles as being along the lines of the combat seen in TWoK.
Does anyone else like those old covers, to the point of letting it influence how a novels events look in your mind's eye when reading them? Anyone a fan of those pulpy, sword and planet, wildly "inaccurate" covers from the earlier decade? I say "inaccurate" in quotes because, even though I know there's a tendency to prefer regarding ST as having one (or as few as possible) continuity or universe, the novels kind of do have their own continuity, their own version of things (different cultural depictions of Klingons and Romulans; different historical details, especially with Strangers From the Sky and Federation). It seems to follow that there's room for having it's own visual identity of oddly mixed elements.