Urban Myth
Oh come oh Lester, this is one of the better known modern urban myths.
Think about it - what is wrong with a SatNav leading the crooks to your home? They can't be sure that the house is empty (grandma may not have gone with you, or worse for them your husband who is a police officer and just got home from Judo training). What do they expect to get their that they can't get elsewhere? They don't need the keys to the car they have just stolen because according to your story it was a dash-mounted job and so they must have driven the car there! Also, there is a good chance that the only keys you have for the car are in your pocket, not at home. And thieves have a much better way of getting keys and car together - they break in at night when the car is at home.
Not only this, but if this were a serious problem catching the thieves would be easy - as soon as your SatNav or SatNav-enabled car is stolen just give your address to the police and they can pick up the miscreants there.
Oh, and how useful is a postcode for finding your home? There are about 12 houses that share my post code, but many places have even more!