I have no problem with ex pollies and PMs on the speaking circuit but I think it depends on what it is in regards to Boards. For example if you look at Julia Gillard's Board appointments they are The Global partnership for Education, Beyond Blue, The Institute for Women's leadership, Campaign for Female Education etc. I think these are examples of what ex PMs can do to keep adding value to society. Turnbull is involved in young IT businesses which is probably fine as well given his background. I can't imagine that Gillard in particular is earning a fortune from her Board appointments.Howard, Rudd, Gillard, Turnbull all earning plenty on the public speaking circuit and for their "contributions" in the media.
Gillard is on several boards as is Turnbull.
All earning an absolute fortune whilst being paid +$200k + expenses by the taxpayer.
What I don't like is when ex pollies sit on James Packer's Board or mining companies or Banks or Telstra as examples. Industries that lobby Government heavily and who would benefit greatly from inside information and contacts.