Just because people are willing to pay for it, doesn't mean it's is not over-priced. What you're referring to there is what is affectionately called a "bubble" when it happens in financial markets. It basically means that there is a perceived value that is higher than something's actual value. Invariably the used price will fall as people get smart about it, but the people paying those prices now ultimately are the ones that lose out, as they are buying at the top of a curve that is likely to shift downward.
There is always lag between actual value and perceptual value. If, in fact, the new 5D2's are going down in price and the used market isn't moving yet... then one most certainly wants to stay away from the used 5D2s right now! That is, if you're like me and think of these things as investments.
Your perceived value is the only thing that matters. That IS the market value if that is what people are paying. It's easy just to say they are uninformed just because you disagree with a market value of the item. I could make that argument against everything you have purchased. Now that doesn't mean it is that valuable to me.... I bought my 5d2/24-105 kit witH 40 clicks for $2400. I happen to think BMW's are way overpriced based on what one gets and their reliability, but the public buys them so that is the market value regardless of what I think.