It was so much power and torque back in 2004 many wondered if AMG had gone too far. The cars featuring the engine (the S65, SL65, and CL65 AMG) were absurdly expensive. The other absurd part about these cars was their depreciation. The CL65 AMG depending on options was a $180,000+ car back then. Today, you can pick up a nice used example in the $30k range. The car was not an investment that is for sure.
What does this money get you? A twin turbo V12 luxury rocket with 528 horsepower and 674 lb-ft of torque to the wheels. A simple ECU tune will bring those numbers up into the low 600's to the wheels for horsepower and close to 800 lb-ft of torque at the wheels. A quality tune will run you a little over a grand.
If that is not a tuning value BenzBoost does not know what is. The only problem really is the maintenance as the coil packs tend to go out and there are well known issues with the ABC (Active Body Control). These issues can be solved with proper maintenance and parts.
Getting more out of the car beyond a tune becomes tricky due to the turbos being integrated into the manifolds. The K24 turbos on the motor are popular in the Porsche 911 Turbo world and easily modified but the problem is getting to them and removing them. Turbo upgrades therefore are expensive and there are not many successful upgrades out there.
Keep in mind the 'modern' M279 twin turbo V12 Mercedes sells is basically this exact same motor. Yes, this basic twin turbo architecture is providing over a decade of service. Why overpay for a new version of the same thing? Pocket the change and have an AMG monster for a fraction of the cost.
It's hard not to love 800 lb-ft at the wheels with a tune (tune by Eurocharged on a CL65):