[danb35]

Well, the shorter (10 cm) set of wires arrived rather more quickly than I'd expected, so I tried hooking up the display to the board with them. No change--I'm now getting just a solid white screen. I think the wires themselves can be reasonably excluded--I've tried two different sets at the 30 cm length, and one at the 10 cm length, with no change in results. I've ordered another display; hopefully it will get here soon.

I've taken a couple of traces with MOSI and SCL showing--MOSI is in yellow, SCL in blue. Here they are: