I sold my C55 for a 996 Turbo, purchased the Porsche in July 2014 for 23k, well maintained with 3 previous owners, stock with no modifications.
Today's market price is probably +10k or more on my purchase price, was offered 35k this time last year.
I personally believe that certain cars are subject to this appreciation, which no one can predict, who knew the 996 Turbo would demand the money they can today, not even classed as a classic really.
My purchase wasn’t based on future values, it was an awful lot of car for the money, much the same as the C55, I’m just lucky really, I had an idea they may appreciate in value based on other models coming into a renaissance but it wasn’t my main reason for purchase.
There are a lot of N/A 6.2 liter Merc engines about in various models, the 996 Turbo engine is used in the 996 GT3 (albeit minus turbos) and the early 997 Turbo, all 3 demanding higher values.
The 996 Turbo is still a wonderful car to drive, very engaging and typical Porsche characteristics, I’ve driven the C63 and it’s an enormous amount of car, bit of a wild stallion in comparison to most everything close to its class, I would hope this alone would be the demand point that may help it become a high demand car in the future.