The "Default Thread Subscription Mode" at http://www.flyertalk.com/forum/profi...do=editoptions
allows you to specify instant email notification if someone replies to a thread where you have posted. Other boards seem to set this to "instant email notification" for new members. That would build engagement.

A more focused version would notify the member only when his or her post was quoted in a reply.

As to the "Helpful" button we discussed last year, I continue to believe that it's worth trying if the software can be modified to deploy it in selected forums only. A sitewide time-limited trial would be a distant second choice. Last year's discussion thread was outstanding for the range of issues it covered.