The internet has a lot to do with the way people modify their cars, or even the cars that they buy. The latest craze seems to be to get into a supercar/supercar performance territory as young as possible, brag about the numbers (money or bhp), post YouTube videos purporting to be footballer-scale wealthy and let the rest of the world speculate about what you do for a job and wish to be you. In reality they all seem to live at home and have a great deal of finance, but then again if your aspiration is to never own your own home, spending 80% of your monthly income on a car repayment is a personal choice and perfectly acceptable; do with your own life/money what you will. This lifestyle sells to the viewers and before you know it, another YouTube channel pops up doing exactly the same thing again by someone else, because the Internet said so.
Anyway, I'd certainly say that adding a remap/headers to an M156 C63 isn't a daft idea whoever you are. If you know even a little about the engine then you'll come to realise that the same one with minor differences was used universally across many AMG's of the time and performance varied based on a couple of components restricting the true performance potential, which the engine is naturally built to produce, and are easliy released. The final output doesn't seem to be any different when comparing Performance Pack (light camshaft, piston and roads) and non-Performance Pack cars.
A remap for example releases the ECU restriction on horsepower, which is limited by the ECU only allowing the throttle to open a certain portion. This was allowed to open further on Performance Pack models in order to increase the power, and further again for the 507 models. A remap bypasses all three of these stages and allows as much as is safe with no hardware modifications.
Now the headers. I'm not sure if they were made purposely restrictive or to comply with emissions and noise regulations, and there's probably some manufacturing cost saving to blame there too meaning they came out less than perfect for the engine. Aftermarket headers remove this problem and on their own without a remap will increase performance, but with a remap allow the engine to be the best it can be, naturally aspirated with no internal mods (cams or more fueling for example).
The upside/downside with headers is that they release a hell of a lot of engine sound. Coupled to the stock AMG exhaust system you are coming close to NASCAR levels of noise when you're "on it", otherwise it's still fairly civil in town. This is why a majority of people also buy a valvetronic rear silencers which are more robustly sound insulated than the stock AMG rear silencers. With valves closed and headers fitted, the exhaust is around as loud as a stock C63, maybe quieter but, with valves open it's louder still than a car with headers on the stock exhaust.
