Idea: Have native Spanish speakers explain errors (e.g., in grammar) in lessons made by English speakers and vice versa. The quality of help received would depend on the quality of help given.
If you are particularly helpful, then the person who received your help would indicate that they want your help again — which increases your helpfulness score. A higher helpfulness score in turn allows you to receive help from people with higher helpfulness scores.
I would argue that having a low helpfulness score shouldn't preclude help from very helpful people.
Perhaps helpful people should have the questions presented to them sorted by decreasing helpfulness of the owner (and followers) of said question.
The more helpful people would still be able to see the questions from the less helpful people, they would just have to scroll a little longer.