Update: well here's something bizarre.
I decided that the problem, perhaps, was in the GLaunch.sh script, so I typed up a GBackup.desktop file and copied that into the ~/hildon folder. When I executed the GBackup from Extras, I got a gvm-backup.tar file that was only 10 kb in size.

I then deleted that file and executed the command directly in XTerm:
tar cvf /media/mmc2/gvm-backup.tar .gvm

After that, I got a gvm-backup.tar file that was 576 mb in size (the command also backed up my eight alternate gvm.store files).

Now this script and *.desktop file thing has got me really confused!