Hello Falcon.
Mini-events are smaller unannounced events, they rarely move the story forward, and rarely have rewards (I do not consider books rewards).
A Mini-Event is really just an event format that lends itself to creating a living breathing world as opposed to a scripted one.
Anything overly important, and major plot elements are almost always announced (like the one I posted today).
Mini-Events are also a tool for me to simply run an event when I have a couple hours. They are fairly one dimensional, (ie: Evil Necromancer animates a graveyard!)
None of my events are designed for every player to attend every event, its just not possible, with my schedule, your schedule and the 12? different timezones. This is why I strive to always post recaps of events, and important plot elements and why our stratics reporters are awesome.
Do not get discouraged, these past 3 events have just been plot devices for me to get the 3 encoded books into the hands of the public, there is a thread on the main Atlantic board (That I cant reply to because its not here on the EM board!) involving the cracking of the three codes.