Well, I drive for a living at the moment, I go all around the country and I do now know the routes so I don't use my SatNav, for good reason.
IMHO SatNavs are a complete waste of time, my Garmin is "up to date" and a new model - even though it still doesn't recognise new roads/layouts and even told me to turn down the wrong way of a dual carriageway in London once! Absolute death traps. It still isn't updated, road works on the M62 and M6 (some parts) have been finished for years, but my SatNav STILL tells me theres a 50 MPH average speed camera zone - thats why when you see some people going 50 most likely, because of their stupid SatNav.
I'm speccing an A3 soon, and am leaving the SatNav option, I know the bigger screen is nice but I simply do not believe it's worth it, i've also had a few SatNavs before that and they are absolute pot. I'd stick with a SatNav off Amazon or wherever, £500 is a lot of money on an option you might use few and far between, and spend most of the time swearing at it especially these live traffic updates, they are as bad as the gantry signs on the motorways, absolute useless. "Slow down - accident" - you get there, theres nothing there... and when they don't warn you and say everything on route is fine - it's not and theres a complete **** up - i've had that countless of times, my SatNav also says that M1 + A50 + M6 is the fastest way to Manchester from where I am, no, M6 is, just M6 - I save about 15 minutes when I ignore it and go M6, how does that justify when I've set it to the fastest arrival time and it's taking me the slowest - i'll stop now because I can carry on ranting for hours but you get the picture.
Unless your driving to new places all the time, i'd personally leave it, also I think you have to pay ridiculous amounts of money to update it - £200 I think, maybe not, Audi might be different but i'd look into it first. Frankly, if you want it purely for the bigger screen think this: if they wanted £500 off you for the bigger screen only - would you pay it?