I know they were planning to introduce the Cloud city and other cultures that were already 'known' in TOS. I loved the mirror episode (and not just for Linda Park in that outfit) and actually thought it got good after they left the damned time war behind.
My honey's a ridiculously-avid Trek novel reader, so I can ask for specific post-TV Voyager recommendations, but I believe that the stories you want are published under some of the 25-50+ years-ahead-of-TNG, book-only series.
** spoiler omitted **
Just wanted to correct myself- the DH says that (a) the post-Voyager books are only a few years ahead of TNG, and (b) the Voyager crew is included/featured in quite a few of them. So happy hunting!
