Having owned a few...
The w202 especially the sixes are brilliant cars.
The w203 from 2001 until the facelift isn't a very spectacular car. Lots of hard cheap plastic and the interior isn't exactly up to Mercedes build quality in my opinion.
The w203 from '06 until the end is a BRILLIANT car! I may be a bit biased because my c280 Otto saved my life though. The sot facelift cars have smashing modern engines backed by the solid five speed auto. The facelift took care of the quality issues and the interior became a much nicer place to be.

My most recent experience owning a C class has been a very pleasant '10 C300 which my mum bought new and ran up to 30k miles. It was a good performer (same 3.0 6 as my 280) and the 4matic (lifesaving component on Otto the 203) was a very nice feature. Despite all this the interior felt smaller, but I'm rather tall. Her car was from the South Africa plant, and I was curious how it would hols up as all my other mercs are German manufacture. I personally believe that the bottom of the market Benzes are falling prey to Planned Obsolescence. Mercedes from the 1980's and back were cars built to last many human generations with proper care. I do not find this to be the case with the modern incarnations in the lower price bracket of Mercede's product range.

Point in case, search for news on the new C class and you'll find that MB plans to build US models in it's Alabama plant with Nissan engines from a Tennessee plant. Mercedes prevailed into the 80s as leader of the pack because it was a Swabian (local German) company doing business on a global scale. Now, it seems in order to stay alive Mercedes is diversifying to provide cars for lower income individuals who are desperate for the perceived Mercedes style and their heritage of quality. This is why the C class exists, to fill a profitable market demand so that Mercedes may continue to build it's more uncompromising models, such as the E, S, and SL models.

Long story short, with Mercedes being what it is today if you want one of their real cars you have to pay E class money and up.

Since the OP was talking about the tarted up C63 I offer the following; if you're laying out eighty thousand dollars why not think about the '12 E550 cabriolet? With the new twin turbo engine it's bloody fast (4.9 0/62kph 13.3 quarter mile!) When mum went to replace her C class Heidi with something infinitely nicer she went with an E550 cabriolet and it's one of the nicest cars we've ever had! With the E compared to the C63 you get essentially the same performance, a couple **** hairs on the zero to sixty. And if you're buying it for the track there's always going to be someone faster than you, so why not enjoy the ninety six million miles of headroom offered by the cabrio, instead of the marginally better performance of the cheap class?