Here's a playlist of every single Event gotten Platinum. Every video has a strategy written there as well as some commetary from the creator: oldskoolradio. All credit goes to him!
Playlist:
http://www.youtube.com/playlist?list=PLDDF3CE17727AD475These videos helped me out immensely! One example: At the end of Center of Power he does an upward air dash, that saves almost 5 seconds!
Another very good tip that helps a lot: For the Kill event where you have to kill military, you can bring tanks from Free Roam mode and place them near the event area. Damage them a little, and when you destroy them during the event (even though there's no enemies in it) you will either get 10 or 5 kills added to your score, depending on the actual event. This trick was a lifesaver!