In my personal opinion i dont see the need for a 2nd airport. They should get rid of the 11pm-6am curfew and spend the money on building new roads like the F6, improving public transport and improving roads.
Even if Sydney airport gets that congested surely they could raise landing fee's on narrow body aircraft to try and encourage airline's to use widebody aircraft.
Even if they do build a 2nd airport it probably will be come !!!! rip off like everything else the NSW government builds like that "2 lane" cross city tunnel