Update- success, though still somewhat a mystery. I copied my /texture and /effects folders out to a temporary location. I confirmed I was on the latest release/hotfix, but re-downloaded and reinstalled the client and content components. I ran a file comparison between the two and, aside from the additions placed there by add-ons, I could not see any differences in the stock files (size, date, etc), so unfortunately couldn't identify a culprit.
I've run through my various add-on aircraft and scenery and see nothing amiss. So, simple answer was reinstalling the client and content;