They rarely showed up and they were exploring that part of the Galaxy.
I don't recall anything overly fanwankish in the handling of the Enterprise in Vanguard.
They had zero to do with the story, nothing. We got like 2 or 3 chapters with Kirk upset over an unrelated event and thar whole odd thing with Scotty and Gaz or whatever the crime lord was named.
Nothing was relevent to the story. They just kept bring up TOS events for fanwank reasons. IMO it really took away from the books.