It just may be that Porsche made over 100,000 997 cars from what I've read.
That's more than any other 911 built in the past. The more they make the faster the deprecation.
I just sold a pristine 1997, 993C2. The money I got afforded me the opportunity to buy a 2006 997S with only 7,000 miles. I bought the 997S for the exact money I sold the 993 for, $50K.
I debated for months with my decision to sell my car. After driving the 997S for a month now I can say I've almost forgotten about my last Porsche.
The 997 is really a great car, minus the gas mileage. I looked at the 996 TT but didn't care much for it. The 997 feels very close to the 993 in it's visceral feeling.
I didn't buy it expecting the prices to rise like the 993 have done. I love all the creature features I didn't get in all my past P cars. Heated seats are very pleasant as just one example.
I've owned numerous P cars and actually don't understand what the big deal is with air cooled cars, other than the sound. With a water cooled car I can now drive a car with an AC that works like my Mercedes. No more need to turn it off in traffic.
Want an investment car, by all means find a stock 993, bubble wrap it and put it away until the speculators realize they are over paying for them. I will always feel the 993 will go down as the sexiest 911 ever built for us mortals. No disrespect to the RS or GT owners.