Please keep in mind that not all of us are masters of the challenges and have completed every one of them yet :p
I am still just hoping they will allow higher limits - Nothing "burns" me more that having to lava items like cactus, especially when I would love to have more sand.

 

well even if you have just completed a fraction of the challenges yet, you either can probably complete them again easy way and get rewarded again or you have only completed like 2 or so which wouldnt hurt you either if they get reset.