For you, it has no advantage. You have integrated all js by now and you avoid the common mistakes instintively.

For me, it is the gray area, I am a language geek so the semantics of js are quite clear but js bytes me sometimes. In coffeescript, The syntax is better and the semantics are better exposed , so it may be a net win.

For a guy who is already familiar with coffeescript, the change will be likely negative. Familiarity with coffeescript is likely to generate bugs in javascript. You're moving from one language to another after all. The impact won't be huge as the two are quite close, but there is no reason to change in the first place.