Restricting Event to Logged in Users

Is there a way to restrict an event to only logged in users? The only way I can find is to use Protection on the event and assign to all users that are in the system or to a group that I assign all users. Is there any other way?

No, we currently have no way to indicate “all logged-in users”.

Is there a way to give users a default group as they are added to the system?

Writing a plugin to do so would be quite easy. But not out of the box.