Hi Sean,
Thanks for your feedback and suggestion. We've found that people use private Q&A for asking questions they don't want public, but also when they want to make sure they get an answer (an answer is not guaranteed in public Q&A). We actually do see identical questions in public and private Q&A from the same person, as they seek an answer from an SEOmoz associate. When SEOmoz associates have more time to devote to public Q&A, they'll be able to answer more questions, and endorse and clarify existing answers.
We are looking at adjusting which questions are indexed in public Q&A, but it would be along the lines of only questions that are marked a "good answer" by the original poster or have an answer endorsed by staff would be in the index. This would help make sure that people coming in from a search engine would see just questions that have good answers. I will pass your suggestion along to the team to see if there's a way that could be TAGFEE for us.