It seems unclear, personally I doubt it, that such a contest can improve the this site in the long run.
If this site will be succesful, then it will be due to a broad community of mathematics teachers contributing to this site a bit out of personal conviction, not a couple of power users contributing a lot. There is already a lot of gamificatioon going on an SE site, which has some good but also some risk to it see The problem with extrinsic motivation, I do not see a need for more.
For this site, perhaps more than for more technical ones, I think we should really optimize for breadth and not focus too much on high-lighting extremes.
The contest there also had a component of giving credit for promoting this site. This might be relatively more useful. Yet, it also seems very premature. At the moment we are still in private beta. Let us wait what happens if the site "opens." There is also a risk in too rapid growth, and in any case at the moment most everybody will anyway be motivated to do things, as the site is new (and thus exciting).
More generally, personally, I am not that convinced of the usefulnes of such 'contests' and related things for longterm goals. It somehow sets the wrong incentives and one runs a risk of achieving less: one starts a sprint, one progresses fast, it is great, then one is tired and takes a rest, and perhaps gets frustrated nothing is moving now, and so rests a bit more and more. Had one just continued walking all the time one would have gone further already.
Of course, there can be times when inducing some extra effort can be useful, such as for burning down a giant queue, but for the longterm developpment at the site at its very start, in my opinion this is not the right approach.
Perhaps if at some point in the future it should seem that things slowdown too much, while we are still below a critical mass, then might be a good time to induce some extra effort via some "contest."