[Perfectlap]

It has little to do with the styling and merits of the 996 and more the sheer numbers that have been produced and are rolling about vs. the paltry number of air-cooled 911's that are currently available.
Which is the grand irony, the 996 was a monumental, game-changing success for Porsche even after the dot.com crash where many deep pocket buyers lost a colossal amount of money putting us in a sharp recession. Meanwhile during the great boom economy of the 1990's, the greatest bull market since WWII up to that point, Porsche could barely sell 1,600 air-cooled 911's in all of North America for its final year of production.
Porsche of Miami probably sold that many 996's in a single quarter. But fast forward to the present and the second hand market is up to its eyeballs in 996's, 997's, 986's, 987's. Which makes these cars worth very little as the costs to maintain all of them is far out of the reach of most second hand buyers. The air-cooled 911's don't suffer from this problem because there are simply more buyers with means than there are vintage 911s.

As far as the 996 as a car, it's the workhorse 911. It was the first 911 that could put the average weekend warrior within a matter of seconds of the most experienced factory driver all with little maintenance compared to many previous 911 generations. It was the first 911 you could drive every day, year round and not face costly engine rebuilds as regular part of long-term ownership. If they engine let go, simply buy a crate engine and your on your way.
Had the Porsche design team simply introduced the 996 with the 993 styling of high fenders, round lights and a short wheel base, but with a water-cooled engine instead, the 996 might not have sold as well. Think about that for a minute. That's how low the reputation of Porsche had fallen relative to their high asking prices in those expensive 1990's dollars. People were buying two of everything in the 1990's yet they little if any interest in Porsche, even those who could afford them. But if you talk to people these days about the 996 it's like if this was the car that nearly bankrupted the brand. How's that for gratitude!