Other ideas in case they haven't been considered:
Would the Gazettes at Archive NZ have appointments of lawyers? Might they have some of his cases there?
Would the Davis Law Library have a photograph and further information about Edward?
Ancestry will show you where Edward and his wife were registered to vote
http://www.rootschat.com/links/0g2m/Have you contacted the Auckland Museum about a photograph? I looked in the Heritage Collection that Auckland Library have online but nothing jumped out at me.
http://www.aucklandcity.govt.nz/dbtw-wpd/heritageimages/index.htmNot sure if I am telling you what you already know but the probates will list children, if any.