Hi Martyn.
First of all, welcome to the club. Hope you enjoy the world of Lexus motoring.
Secondly, I am not sure I understand your particular problem. I have a first generation sat nav system in my old Merc, but it transports me to a village in Spain via a variety of routes, twice each year.The fact that it is not updated need not be a particularly serious problem, so what exactly do you need an expensive updated system for ?