90% success.
I uninstalled MC28.
I reinstalled MC28.
I restored my license for MC28.
I created a new Library on my local hard drive (that way I could leave the default Main Library alone).
I imported a single Movie. I imported a single Series. I imported a single Album. All those worked.
I imported my Series folder (all my TV shows). I Imported my Movies folder. I Imported my Music folder. All those worked, mostly.
Still some weirdness.
I lost my [Episode] ratings for a couple of [Series]. Also, in the Tree, when I expand [Series], each series is missing the "sub-folder" for each season. I used to have that. The [Season] and [Episode] Tags are intact, so I am hopeful MC28 will build those subdivisions in the Tree while I'm not looking. But TV Cover Art displays correctly now!
I lost two Movies, but that happened several days ago. Also, not all Cover Art displays properly despite being fixed over the past couple of days. Very strange. I have experimented and Get TV & Movie Info works properly (no destroying .mkv files!), so I have that to fall back on.
Thank goodness all my ratings for my songs appear to have come through. Also, even though the one (Multiple Artist) Album I imported "singly" didn't import properly, when I Imported the entire Music folder, all of my (Multiple Artist) albums appear to have imported properly. Only one "entry" in the Tree -> Audio -> Albums view, as it should be. I also found four Albums I thought failed to Import before I started all this. Turns out the tagging is abysmal and they ended up in Unknown. I didn't see them there. I started fixing the tags, and am looking forward to the new Clean() functions being worked on.
I need to configure Auto Import. I need to reread the thread or Wiki article about scheduling Auto Import when MC isn't running.
At least I think I read you can set that up. I think I have my default folder structure entered properly. I have a half-dozen small SmartLists to rebuild. I may try saving the .xml files to Notepad and cutting and pasting as terry@tassie has suggested. I've not tried that before.
I also want to try setting up two zones and zone switches. I think I can use those to route Audio-only files through a USB port and Video files through my HDMI port.
Oh, yeah, I have to repair my USB drives to act as secondary back-ups to my NAS (hopefully correctly performing in RAID 6 configuration).