Yeah, Bruno has got a point here. If an exam has many unrated questions, maybe it could give more points for rating than creating new questions, balancing the situation on each exam. By doing so, exams with no questions would give many points for new questions until there are many unrated questions. When it happens, rating a question could give more points than creating new questions. I guess this would also speed up the creation of new questions.
Also I guess the more basic exams would give less points for new questions as I suppose they probably have many new questions authored by those who don't know very much about advanced topics and will make poor questions.
I agree with you on the fact JBB platform should automatically propose the most useful contributions to his members. That's a core part of the new moderation process (as far as I know). We could pay more for what is more useful (idea of the existing bonus factor on some exams)
But we'll not give too many points for voting on questions because it'd be too easy to give any rating quickly, just to get points, and because we even might suppress the voting system in the new moderation process.