I understand the cost factor involved, but the whole experience lost something for me after they stopped using actual Star Trek actors.
Same here. My main reason for buying them was for a new performance by ST actors, often "in character", with music and sound effects, that I'd never experienced before. I didn't yearn for "unabridged" at all; if I wanted the whole story, I'd rather read it myself (and I did).
In fact, although I have every other ST audio, I never actually bothered to track down the three unabridged "Vulcan's Soul" books, as read by Richard Poe, put out by Recorded Books
, 2004, 510 min; 2006, 630 min; 2007, 694 min, and I've never found the time to play my CDs of Zachary Quinto reading the 2009 movie's unabridged audio of the Alan Dean Foster novelization.
I can't believe that if even Trek Audiobooks were poor sellers back in the day
They weren't, but sales must have started to flag about the same time as they reduced output to mainly only the hardcovers, and then dropped the ST actors in favour of narrators from the regular S&S Audio stable. The gamble was to move to unabridged, or just make fewer abridged per annum. I don't think Recorded Books set any worlds afire with sales, though, and those three were available on CD and as downloads.