Quote - However, more serious (to me anyway) is that I've now had two spherical terrain scenes crash AFTER I've exited the Options menus and done work on them.  One of these files had several hours worth of effort put into it and I would GREATLY like to recover this file.

I had a similar problem 2 weeks ago and sent e-on the problematic file, which they couldn't open either.
Yesterday the newest beta release of Vue 8 was available for download, and it loaded the file without problems. Dunno if it's because MY particular problem, but they somehow fixed it.
As soon as this beta is available to the general public I'd give it another try, so backup your corrupted file in case you should need it.