I think that the books "Battlestations!" and "Dreadnought" by Diane Carey have a prominent Mary Sue in them, but I haven't read those either, so I'm not sure.
We've just been discussing that in the "Your least favorite Trek book" thread (starting around post #75). Piper is an author surrogate, but doesn't really qualify as a Mary Sue for reasons spelled out in that thread.
I guess the 'Mary Sue' aspect that stuck out for me was that, yes, Cabot was a featured guest character, and especially how towards the end she seems to be way too capable (when she's on the Androssi ship for example). That, and she's "something else" and instantly intriguing to most of the other characters she encounters (albeit not always in a good way, initially).
If you have fudge and qualify the definition like that to fit a given character, then that character probably isn't a Mary Sue. Too many people use the term simply to mean "a character I didn't like," regardless of its genuine meaning.
Maybe it's just that Wesley seems so naturally to be a Mary Sue type of character, but Vornholt certainly didn't shy away from exploiting some of the Wesley story cliches.
I don't think that's fair. The series established that Wesley evolved beyond human form to become a Traveler. It would be absurd to bring such a character back and
not have him manifest exceptional abilities.
You can't just cherrypick the aspects of the definition that suit you and say "Yes, this is a Mary Sue," because any individual aspect of the definition can also apply to non-MS characters. And even if the author who created a character did so in a Mary-Suish way, that doesn't mean that every subsequent author who works with the character is using him/her as a Mary Sue.