I do like the Núr edition but like you say, they lack in comparison to their competitors. The interior is pretty much what you get inside of a van. As well as the statistics.
But they do sound nice
The RS is forking out a lot more, in respect to a few more. Personally, I don't think the RS is worth the 19-26k. Fast cars wear off, and fuel bills do not.
You should balance out fulfilling your need for speed as well as not emptying your bank account for the next five years.
And this is just illogical advice. You'd be lucky to find a c63 on an 07 plate for less than £25,000. Then insurance, fuel, services, MOT, random breakdowns.. I wouldn't like to own one of them if I wasn't topping £100,000 a year.