How about posting a poll of requested/potential new features to guage the number of people who would be interested in them?  I think it should be somewhere other than the discussion boards.  How about using the poll on the home page from time to time for this?  Maybe list 5-10 items and ask users to rate (not rank, but I guess that might be useful too) them on a scale of 1 to 10 as to how desireable each feature would be?