anytime someone wants to go on a box opening spree expecting to get an unusual, I always send them to:
http://www.youtube.com/watch?v=po0fv-NgiIA
http://www.youtube.com/watch?v=Pz-xXL63l5c
Strong coffee. Some do get lucky every day, but it probably won't be you. AND, consider that even if you open 50+ chests and get an unusual, it may not be the unusual you decided to start opening chests to get and could be worth less than the keys it took you to finally get to it. Not to mention the excess of duplicate items you now have to find a way to sell to recoup at least some of the investment.
I always open a couple, but not with the hope of getting an unusual anything because it's extremely unlikely. If it happens cool, but that's not the goal. That's a fool's errand.