I think that's a normal depreciation curve for that car. In the realm of $100k+ luxury/sports cars, it's actually holding pretty well. the thing you need to consider is that the primary market for those cars is the new car market and they sell to people who can buy them like a pair of socks, they would rather pay $20k over sticker for the newest/baddest status ride than have last year's news. That new Audi will be the hot car for the next couple months here, then cool down.
A 5 year-old 996 turbo w/ some miles that just went out of warranty and just lost the last of its *new car smell* is worth half of a new one. Only Ferraris and other low production exotics defy this, and usually only with super-low miles.
I would disagree that eBay is not the best indication of value. I think it is. It's the only place where you can see actual trading prices, somewhere like Autotrader is worthless with all of the dreamer sellers and no indication if anything is selling and for how much.
