The script /usr/share/doc/xfree86-driver-synaptics/script/usbhid isn't
working and some parts appear to be missing ($REMOVER) -- or am I
missing something?

OTOH the usbmouse script does what usbhid claims to do -- how about
adding this at the top:

#!/bin/bash
#
# This hotplug script disables the Touchpad when you plug in
# a usb mouse and reenables it when the mouse is unplugged.
#
# Create ~/.touchpad.on or ~/.touchpad.off for manual override.
#
# Copy this script to /etc/hotplug/usb/usbhid to activate.
#
# The script is from the xfree86-driver-synaptics package.

BTW will this be updated to xorg?

Dave