This is more or less all covered by grinder's Mozilla Sidebar status page - which shows the newest nodes with color coded dots for freshness of initial post and last comment, together with the total number of comments.

This is a work in progress, but already very useful.

As a side note, I don't consider the number of replies as the only criterium whether a question has sufficiently been answered. TIMTOWTDI, and you may always be able to add a new (or bizarre) touch. Sometimes the best solution is way down the thread, see Safe for SQL for an example.

--
Cheers, Joe