Wow, we all have bad luck.
For my past four mara KQs I got nothing.
Then I waited for around 2 minutes to open, and I got Sign of Mara (+40 HP), lucky elrue, and some green lvl 14 archer boots. >.>
I was so happy!
Maybe I should wait before opening the chest every time ... xD
Btw, you can get extra xp from chests? I never knew O_o