Tdockery, thanks; it works perfectly! I love you, man. (Platonically, of course.
Perhaps the Caja integration package should be removed from the repos entirely, and the Nautilus integration package should be renamed Nautlius/Caja Dropbox Integration. Of course, as usual, the repos install Dropbox itself in an unsupported location, so when you try to start it, it wants to DL and reinstall Dropbox, but I'm used to that little hiccup.
And heh. Viking, Unity was one of several reasons I switched distros to Mint, and while I like Cinnamon, my ancient laptop with its wimpy Intel integrated graphics seems a bit snappier with Mate.