Mitlov, I am not sure if the 2009 CTS is better than the 2009 C63. I am sure they are both fine cars. Only time will tell which one is better. The CTS-V does do some things better, ie. 550hp over 450hp, slightly bigger - which may or may not be better depending on who you talk to, although personaly I prefer the CTS size. The CTS-V may very well be worth 10k over the C63 but given the state of GM / Ford / Chrysler I am not sure the time is right to position themselves at that price point right now? Then again like you said if the CTS-V is the better car then why not?
I prefer compact sedans to midsize, but all other things equal, compact sedans are cheaper to build. That's the only reason I mentioned size.
Tell me what the C63 does better than the CTS-V. I'm not just talking power and straight-line speed, where the V crushes the AMG. Let's talk handling. The C63 is an out-of-control, understeer-to-oversteer beast. The CTS-V, though, posted possibly the best Nurburgring lap time EVER for a sedan, which you can't do unless you've got great handling as well as speed. Let's talk interiors. The MB feels vault-like, but materials don't impress, and it's nothing fancy. The Caddy's interior is utterly jaw-dropping, and reviews I've read say that the materials are as nice as the design.
...so do you have any reason, any reason at all, to think that the CTS-V is the same price to manufacture as the C63? You say you don't trust American manufacturers, but that has nothing to do with whether or not they should sell an $80k car for $80k (or whatever this will cost).