Well, the 04 has a 6 speed transmission, 5.9 0-60 time vs. the 6.3 for the 01-03, smart key access, updated Nav system, Bluetooth, Rear view camera, updated grille/bezel, but other than that pretty much the same car. That car should last you 5 years without any problems - I too have the silver metalic and it's such a gorgeous color when it's clean!
Congrats on the new LS430! I'll bet you and your wife will have debates over who gets to drive it! Also, with that ultra low mileage, you got a GREAT price!