Having got the connectivity pack in order to get the sat nav prep, I find that there is a use for the sat nav prep even without the sat nav.
That is you can use auto GPS time setting on the system clock.
(I presume that this is done via the GPS in the sat nav prep. Perhaps someone without connectivity could confirm this.)
So until I can afford the SD sat nav system (or rather decide I need it enough to pay for it), at least I can use the GPS aerial (it is also nice to know that it is there).
It's a pity that you don't seem to be able to have both the clock and the digital speedo on at the same time on the DIS (the time is shown on the main screen but very small for my dodgy eye sight).