It's an edge case, but I often find myself writing
  boo.baz((foo) => using(foo))
In this case, omitting the parentheses around the parameter name would make the code easier to type, and actually easier to read in practice (in my opinion, obviously).

I.e., I suggest to allow writing
 boo.baz(foo => using(foo)).
This won't work for multiple parameters (or zero), you will need parentheses for that. It may work with a type on the parameter:
  ...(String foo => using(foo))
That's still parsable and readable.

For function declarations there is no need for this syntax, it's only for inline functions that it makes sense.

(This is apparently also used as "lambda" syntax in C# 3.0).