Actionability. It's starting to be a trend to have the answers be principles, thought patterns, or philosophies. Or wearing off-topic, trying to argue against the need for such a challenge in the first place and cluttering, like in the Elon Musk longevity challenge.
I propose adding a special field, along the like of "title of your contribution", mandatory to fill in! Located after the "contribution text" field. In it, you'll have to propose an action to implement your challenge solution. It should have a small word limit to incentivize a high signal to noise ratio.
The challenge solution should have a clear route to implementation and automatization. So that it's not just "think differently" and "look at it from a different angle" takes.
Underneath the contribution, one could have a button for reporting that the action field isn't filled with something actionable. Moderators get a notification about it and check.
All this would lead to less spammy contributions and hence be easier to go through them all and judge. It would also lead to clearer propositions, simpler to weigh in.