Another note for anyone who is investigating or experiencing this:
As part of my troubleshooting, I removed the bulk of my Dropbox files from Dropbox, and put them in a folder in Documents, which I (of course) called DROPBOX.
Some time later, I needed to save a file from Word into one of the folders there.
WORD CRASHES AGAIN! OFFICE CRASHES AGAIN!
I investigated further, and noticed that these DROPBOX files were not being saved to iCloud (icon of crossed out cloud next to all the files). I checked the folder info for DROPBOX, all fine. I changed the name to DROPBO. Boom! All the files suddenly started uploading to iCloud. Word saves to these folders fine!
I changed the name back to DROPBOX. Boom! Uploading stopped, icon of crossed out cloud reappears next to files. Word crashes when saving to these folders!
So. Something about iCloud & Dropbox's installation in OSX / MacOS is causing Word & Office to crash when saving to folders contained within another folder called Dropbox.
I hope that's enough for other people to be going on with. I'm unlikely to look any more into this.
