No, currently attempting to evaluate () is an error (and a bad crash with no error message, I'm embarrassed to say! [but now fixed and pushed]).
Your argument regarding () is pretty convincing. It's a bad idea. But I find the full-stop notation a bit jarring, not sure why. I'll try it and see if I get used to it... And I didn't want to tread on the "!" real-estate, given that's it's commonly used in identifiers.
I have to say I still lean slightly towards preferring a default of invocation for 0-arity functions, and using the "val" (again, id) function for passing the function itself.
Maybe the best approach is to offer a define-syntax functionality which somehow corrects the anomality (by visiting the AST and reducing without evaluating) before applying the macro transform. But that's quite possibly another can of worms...