You are partially right about C#, my experience with it dates back to the 1.0 version, but even with all these enhancements is it worth spending in the effort of learning two similar languages when you could be learning a different paradigm which will expand your mind in different dimensions and will make you a better programmer. If you are proficient in Java and want to move to .NET why not learn F# instead.
About you comparing CoffeeScript with Clojure is not fair at all. Clojure gives a whole new world on top of JVM, while CoffeeScript is just syntactic sugar for Javascript.