In South Florida, with the rapidly expanding population, it is important to us to update our discs annually. The disc data is up to 2 years old when you receive it. So your 2006 disc has 2004 data. Alot has happened in 1 year. Addresses. maps, poi and others. Plus the increase in new exits on the interstates and turnpike are helpful for planning new routes when travelling on trips.
Dealer is charging you too much for the disc. Installation is simply ejecting the old disc and installing a new one, just like a music cd.
My two cents