[Perfectlap]

No model is immune to over-production. Rapid depreciation has little to do with the merits or flawes of the particular Porsche model.

Once a Porsche is out of warranty, the pool of buyers shrinks dramatically.
With hundreds of thousands of water-cooled Porsches now out of warranty, many with high mileage, there are not anywhere near enough enthusiasts to brave the costly repairs that require specialized labor. Not in this economy. And quiet frankly in the $30K and under buying category, where most buyers are not pro athletes or trust fund babies, Porsche as a brand seems more like a daily driving liability than anything else.

The only real bottom to the prices of water-cooled Carreras, Boxsters,Caymans and Cayennes with this level of excess supply is the seller's decision to simply keep the car (reducing supply): what the market will offer just isn't worth selling since few Porsches are rare productions. Otherwise the average owner, looking for something newer since supply is so good, is going to opt for the quick cash which means prices will continue to plummet further still for all water-cooled/high production Porsches.

Cheap money, making it easier to abandon even two year old cars to the trade-in counter, in nearly pristine shape, only compounds the downward pressure on pricing for the out of warranty cars. Since Cayennes and Panameras are the top selling cars, they will have the rudest awakening once the Porsche premium meets the reality of the second hand market.

p.s.
For certain years since its introduction, a base Cayenne was the cheapest Porsche you could buy, a.k.a. 'entry level' designation. And given its high production numbers it makes perfect sense that Cayennes will become cheaper to buy than Boxsters. The only issue might be practicality, more used buyers need four seats than there are buyers who can do with only two. We'll have to wait and see.