Well you may be right. According to nada.com an 04 g is now worth 130k. A 20% hit from 165k new. But keep in mind, that is if you can find a buyer who will pay it. If a person has the capacity to spend 150k+ for a car will probably buy a new one further driving down the value of used. Because of this, your only outlet to unload the car is at the dealer using it as a trade in towards a new one. The dealer is not going to give you anywhere near nada retail. He has to buy it right so he can recondition it (No matter how nice you think your car is, they all go through this process), then he will retail it at nada guide.
On paper the dealer will show you $130k for your trade. The reality behind the scene, he is only giving you $100k. Thus a 40% depreciation.
This is the unfortunate truth that I have learned after working for an upper-end new car franchise for 20 years.
To test my logic, drive on to any upper-end dealer lot and say something like "I need to sell this car outright asap. What will you give me for it?"
I hope this explains it a little better. An item (not just a car) is only worth what someone will actually pay for it.