Putting Picard or Spock on the cover is a decision that is far more likely to drive sales than the byline.
I was just looking at Reunion
recently, Michael Jan Friedman's 1991 book, and noticing how Picard is very much front and center, but then there are two other people, who we have never seen before, on the cover. But then I've also seen on other Trek books from that era covers where there is a main character (like Tasha on Survivors
), but then there is another character from the story that we've never seen, but they are on the cover. It would be nice if some of the newer covers featured the characters like that---have a main series character (Crusher, Dax, Torres), and then have another main character who we have never seen on the cover somewhere else as well. (Another thing with those early-90's covers I tend to prefer is that they depicted a scene in the story and were painted, with odd novelization cover having a photo or photo-montage on it; the recent Photoshop covers just seem so bland and repetitive and really don't connect to me like the older hand-painted covers.)
But as for Trek having some authors who really didn't know what they were writing about, I think it would be safe to put Robert Shelley at the top of that list. I've never read another of his books, but after reading The Laertian Gamble
, I'm not too sure if I want to track down another of his books, even though he's apparently some sci-fi giant. So, I think that the styles of the authors in tie-in fiction, and who those author's are, does matter, since there are some people where they will only get introduced to that author's style of writing and name through tie-in media like the Trek books.