Thanks heaps for the link, davidfor.
I actually had some success with the dd. After doing it, it kicked into the restore process (I must have corrupted something enough for the Kobo to realise it needed a restore).
However the restore process got into a reboot loop. After hard powering it on and off a couple of times I got to the setup via computer screen. Hooked up into the Kobo desktop application, synced OK, then when I disconnected the upgrade started and then it bricked during the upgrade again. The screen goes really light, then then after a hard reset it is just blank.
AkiraReader's reset tip ( thanks! AkiraReader
) initiated the restore a lot easier thats for sure, and the restore worked first time. After setup via desktop it got halfway through upgrade and the screen went really light again - this time I did a quick power-on (instead of holding down for 10 seconds) and the upgrade woke up and continued. I reckon I tried this before but maybe not. Battery is at 76%, so that should not be an issue, and it was plugged into power.
Anyway, the Kobo has just finished syncing all the books, its been an interesting journey, and I have a happy wife, so thank you so much for your help gentlemen.