Darn it...nothing. No sidecar file in the export location, reimport looks as dark as the export, no history attached to it but I did hit the discard button just to be sure. Things worked just fine in the previous rev for me, so I've got to have something going on here forcing that darker, less detailed look. But interestingly enough, I took in a new photo, did a few quick adjustments and exported it as a jpeg and it looks correct (AND a copy of the xmp file showed up in the folder with it), and I then took the most recent exported jpeg of the starry sky image, did a few things to it and saved it out as a tiff file (surprised I could convert an 8bit jpeg to a 16bit tiff, but I am not really all that familiar with tiffs to begin with - I just use them when doing stacking for the most part). The newly saved tiff also reflect the new changes made.
So I'm starting to think I "broke" the initial set of photos. I do recall running into an error notice about an invalid action or something along those lines during my editing. I had closed darktable, reopened it, and reopened the images and they looked good to me, but perhaps whatever conflicting action I'd imposed was still there and prevented a clean export. Guess I'll have to recreate my edits from the top and see if that solves it!
Thanks again for the suggestions!