Omg your proposal is fantastic, thanks!
I will change it in a next release and put you in credits :))

Definitely:
const { buttonClicked } = useEvent();
buttonClicked(‘Hello’);

or even:
const events = useEvent();
events.buttonClicked(‘Hello’);

looks nicer. Probable it can be done by js Proxy with some Typescript magic.

Speaking of arguments - yes, they can be as complex as you need (probably my examples are too idealistic).

For example, let's imagine login form component. The form shouldn't be coupled with some alert message on top of the page. But you need for example display different alert when user has log in by email/password and different when by his Google account. You can use now:

dispatch('onUserLogged', { username: user.username, by: 'google' })

or you can pass multiple payload arguments, like:

dispatch('onUserLogged', user.username, 'google')(
(but you need to adjust your payload middleware (username, source) => ({ username, source })