I really think your geographical location is a big factor in the accuracy of the prices. I would assume that they would be reasonably accurate in Sydney, Melbourne and possibly Brisbane, but in any regional towns/cities, the lack of competition drives the prices up considerably. Personally, since I live in Townsville, the Redbook prices basically mean nothing to me. I would expect to pay up to $5k more than the Redbook price when buying a vehicle locally.
For example, I keep a decent track of the dealers here and look through the classifieds most weekends. If I was after a diesel 80 Series Landcruiser on any given weekend I would expect between 1 and 4 vehicles to be for sale at dealers and about the same number privately. However if I was in Sydney or Melbourne, I'd assume there'd be at least 5 times that many available. With that much more choice, dealers and private sellers can't charge as much to sell vehicles. So I'd expect the Redbook price to be pretty close in the major capitals. I'd also assume that Redbook gets most of it's data from capital cities.
The trade in prices are a complete joke. There is no way that any dealer would offer anything like the trade in prices on Redbook, from my experience and that of friends etc. Again, larger cities may be different.
Just my $0.02.
matt