1. can an additional camera with a AF live view will do the trick?
I'm trying to understand what you're intending to do. Are you talking about shooting the camera while holding it above your head? If you are, getting a camera with a tilting LCD screen can be very useful. You don't necessarily need a DSLR for this, an advanced compact like the Canon G11 will do the job nicely and complement your DSLR very well.
2. having a backup in a special occasion is a must?
My answer to this is "maybe". I'm personally very happy with covering an event with just one camera. Yes, your camera might break down and that's what the backup is for. Other photographers attach a telephoto zoom to one body and a wide angle to the other, but I've found this approach slighly cumbersome.
3. can a two camera make you improve more? or a waste of money?
You don't need two cameras to improve. You need to take more photos and work at your photography. If anything, having too much gear can be a disadvantage as you're more focused on gear than you are on photography.
4. if you recommend a backup camera what would it be? AF live view is a must for me.
Get a Canon G11. That'll be small enough to fit into your camera bag and you can whip it out in situations when the DSLR is not suitable.