In an effort to get the ball rolling, and before I had read your reply, I reinstalled the Ubuntu Kernel using Update Manager. This brought my touchpad back to life, so a step in the right direction even though I've lost Fn key support again. Appletouch was not running when I rebooted the computer after reinstalling the kernel. I installed it with modprobe and it then appeared in the lsmod output.
After this I installed gsynaptics, edited the xorg.conf to include SHMConfig et al and then logged out from and restarted X.
The touchpad is working still but gsynaptics is telling me it can't access the shared memory area, implying SHMConfig is not set to True.
My Xorg log is also still delivering much the same error as it was before, except this time the Synaptics module seems to load fine, as shown here:
but then the driver goes on to report, later in the log:
(II) LoadModule: "synaptics"
(II) Loading /usr/lib/xorg/modules/input//synaptics_drv.so
(II) Module synaptics: vendor="X.Org Foundation"
compiled for 18.104.22.1682, module version = 1.0.0
Module class: X.Org XInput Driver
ABI class: X.Org XInput driver, version 2.0
I've altered the Device option, assuming the Trackpad to not be located at /dev/psaux but this didn't affect anything.
(II) Synaptics touchpad driver version 0.14.6 (1406)
Synaptics Touchpad no synaptics event device found (checked 23 nodes)
(**) Option "Device" "/dev/psaux"
(**) Option "SHMConfig" "True"
Query no Synaptics: 6003C8
(EE) Synaptics Touchpad no synaptics touchpad detected and no repeater device
(EE) Synaptics Touchpad Unable to query/initialize Synaptics hardware.
(EE) PreInit failed for input device "Synaptics Touchpad"
(II) UnloadModule: "synaptics"