Hard to say. In general any tuning isn't paid when you sell the car.
Also i think 987 cars are more liked by buyers than 986 cars.
At the moment there is a tunes car offered over here in germany. It's a 986 with a 3.6 litre bi turbo engine with 450 hp. Was made by TTP, which is a well known tuner over here in germany. Price is around 26.000 euro - which is around 28.500 USD.
Seller first asked for 36.000 euros. Price is getting down since.
Still not sold.
Porsche TTP Competition GT Turbo 450PS mit TÜV als Cabrio/Roadster in Roding
Regards from Germany
Markus