dd image to clean sdcard
When sdcard written, mount said sdcard and edit /media/pi/rootfs/etc/dhcpcd.conf and insert the static ip addresses in readiness.
Edit /media/pi/boot/config.txt and disable overscan
At this point I checked /media/pi/home/pi and there was very little in it, certainly no /home/pi/.config/lxpanel/LXDE-pi/panels/panel
shutdown -h now
Swap out sdcard for newly written one and apply power.
Pi boots, displays message about resizing the file system and then reboots
When desktop appears, the taskbar is at the top of the screen, so rightclick on desktop, move to bottom using context menu.
Start pcmanfm, check that /home/pi/.config/lxpanel/LXDE-pi/panels/panel exists in correct place with correct contents. Check.
Go through the box of tricks displayed on screen, set the wifi password and then let it check for whatever it checks for.
When it has done what it does, recheck /home/pi/.config/lxpanel/LXDE-pi/panels/panel and find that although the taskbar is still sitting at the bottom of the screen where I placed it, /home/pi/.config/lxpanel/LXDE-pi/panels/panel has been secretly edited to display the taskbar back at the top of the screen, where, had I not checked, it would have appeared on the subsequent reboot. I edited /home/pi/.config/lxpanel/LXDE-pi/panels/panel to make the taskbar be where I wanted it, and then rebooted.
Taskbar at bottom of screen.
Without intervention, it would have been at the top of the screen as it was earlier today when the saga started.
Observations on a brand new install:
Clicking on a .conf in pcmanfm launches libre office 5 which I suppose will edit the .conf, but seems a bit overkill when leafpad is sat doing nothing.
Adding an application to the application launch bar works, but if you subsequently use the main menu editor to alter the properties of said application, but then change your mind and click cancel, the whole thing vanishes.
Wishlist and hopes for the future:
apt-get upgrade is such a fickle beast, if you are 'pi' and you are running default vanilla settings, you might be ok a few times before 'upgrading' means trashing your file system. If you change all the necessary bits to be not 'pi' but another user that takes more guessing, the 'upgrade' does not take into account this scenario and just overwrites stuff and semi-reverts you to half 'you' and half 'pi', which is an untenable situation because your system becomes unusable.
I hope that this behavior becomes a distant memory and that crossing your fingers and touching wood before updating becomes unnecessary as well as pointless.
Congrats on the VLC btw, a lot easier to use than omxplayer.