all good points but i think you need to make new members feel extra special so, to that end, I'd encourage a clique makes pn slightly snobby, promotes brazen but justified attitudes towards photography and allows forthright (with the letter f) opinions. banning references to DxO and their ilk would help.
if one looks at the success of dpreview & flickr & ( in a similar but different vein) the success of the online, as opposed to print, version of the guardian newspaper, the most common attribute is moderate moderation.