Yeah, I understand that, but, hey, why not do it if you'll be playing anyways. Gives me a goal to work towards.
I hope they have future challenges, and that they offer better rewards. Something like Xbox Live Gold free for a year or 1000 points or something. I have to agree, rewards are wimpy, but then again this is the first challenge they are having, probably wanting to test waters before offering something grand. (I hope) Though you've got to imagine, they'd only have a few of the big rewards available, and likely have 10,000 people complete challenge and only 5000 or something get a reward. 50% would be very disappointed.