I'm afraid that in conjunction with significant whitespace, they're not at all gratuitous. For example:
describe 'Calculator', ->
it 'can add two positive numbers', ->
result = calculator.add 2, 3
assert result is 5
it 'can handle negative number addition', ->
result = calculator.add -10, 5
assert result is -5
Mandatory parentheses make significant whitespace lose much of its appeal when passing a block construct into a function. This is a large part of the reason why Python limits lambdas to a single line...
Sorry for the imprecision. It's the same thing to Python, in terms of significant whitespace. Language features that use whitespace for structure are not considered to be expressions, and can't be used as part of a larger computation. In CoffeeScript, they are, and can.
Valid point. Although I'm on the fence about significant whitespace in CS as well; I value fixing JavaScript's glaring flaws much more highly than arguably more convenient but unproven syntax. (The boundary is admittedly fuzzy, e.g. list comprehensions).
Optional parentheses wouldn't be so irritating if the rules for omitting them were universal. Currently, when calling functions with arguments you can omit the syntax, but when calling functions without arguments you must use parentheses. Could the 'dispatch vs variable reference' question be decided with some sort of suffix that preserves the value of whitespace? Something like 'f!' 'g! arg1, arg2'?
