It looks like the problem was chiefly one of there being no good vnc servers on OS X.
Here's a really, really roundabout solution which works better than a 'direct' connection in OS X, ironically....
* The best vnc server for the job appears to be TigerVNC, but
specifically the Linux version. TigerVNC has Windows & Mac viewers too; but the server works only on Linux. (So, no use building it from source, if you're on a Mac.)
Check out their wiki:
TigerVNC. It looks like they're pouring a lot of effort into making the RFB server more efficient.
TigerVNC is also a *lot* more customizable. The most useful customization for my purposes was setting the *color depth*. I set this to the lowest value (8).
It creates a virtual desktop, allowing you to run whatever window manager you like on it. I find twm somewhat annoying, so I went with OpenBox; it works amazing.
In my setup, Linux Mint runs inside a VM. (Side note: It looks like some distros don't 'play nice' with TigerVNC; it works great so far on Mint.)
I first ssh, from OS X into Mint(VM), forwarding Mint's 5901 to OS X's 5902.
I then ssh, from the Kindle into OS X, forwarding the Kindle's 5903 to OS X's 5902.
I then run kindlevncviewer on the Kindle, with the setting
-encodings hextile, to connect to Kindle's localhost:3
I then run OS X's built in vnc viewer (Command-K from the Finder, then enter URL) to connect to localhost:2.
I control the mouse & keyboard from this second vnc window on OS X.
It's a shame for the Mac, really, that this works better than a native server.