I support the idea of a Helpful post button because it adds a qualitative dimension to the post counts, titles (Evangelist, Legend), and program affiliations which members may use to assess a post's credibility. Positive reinforcement encourages more of the same, and this tool should increase engagement of members who are high quality, but infrequent, posters.
I agree with this sentiment. On other forums, "Helpful" is one of the things I find useful - I have no need for "Like". In theory, is the difference between real answers to questions and flaming-run-amok.