It seems like the removal of parenthesis is a bad idea, because it's bound to create a bunch of inconsistent code. Notice how all the rest of the code samples on the page keep the parenthesis in?
I approach this the same way I approach Ruby... I only use parenthesis when they improve readability of a confusing statement or are required (function call with another function call-with params-as a param). As you can see, this statement required parentheses ;-)
Yeah, I'm undecided yet as to which is best. My colleagues seem to be promoting keeping the parens in. Typically when we try stuff like this I like to push it to the max to see how it feels, then scale back.
I find it's a good smoke test for readability. Use parens to bind up atomic expressions in a line. If there are too many parens on a line, it's a good sign that you should break it up into two instead. It wouldn't be better lookin' with more.
It does create some inconsistency (even though CoffeeScript is in many ways one of the most consistent syntaxes I've seen) but you gain a lot in readability sometimes, and it makes it so easy to craft great domain-specific languages.