There is really no reason to think that you have calculated the good value cameras here. What is more likely is that you have calculated the *bad* value cameras--the objects that have lost the most relative value would normally do so because no one wants to buy them; things that are desirable maintain their value. My Leica M4s cost around $400 new, and now they sell for c$1000 and more. That makes all of your Nikon examples look like serious losers, some much more than others.