There's no reason to shout at the list subscribers, this won't make them more inclined to attend. Sentence case, with both upper and lower case letters works best. I only accept announcements via email. Besides it's better that you write it since you know the details of your event better than anyone else, plus my spelling is atrowshus. Generally I send an announcement to the list the week of the actual event.
Most people have a very short email memory.
Of course there are exceptions for events that require some travel or otherwise need some lead time. If you send an event to me the day before or day of the event, chances are it won't get posted if I already have a bunch of stuff in the que for that day. I'm really conscious of list traffic and people who plan ahead get preferential treatment.