I've realised that my original board done in DipTrace had a pretty serious mistake, at least for my purposes - I'd used 0.1" header instead of 2mm, and the standard cables for these displays, widely available off eBay, use 2mm headers. Since I was going to have to redraw it anyway, I've redone this layout in Eagle (which does a better job of differential traces anyway) and uploaded it here:
I have literally no idea if this board works - in fact, after my last screw-up on the board layout, I imagine it's a safe bet it doesn't! - but if anyone wants a look or to use it as a basis for their own boards or whatever, go right ahead.
PS. I rather doubt that the USB header will work well, since the impedance of the PCB will be well off what the USB spec requires for USB 2.0 - it's tricky to get this right on 1.6mm 2-layer board when you have the signal coming from tiny narrow connectors too. I'm sure someone will be able to do a better job of this than me, but it's a start.