I wont bother arguing with you on wind farms viability except this -
every free (almost) unit of electricity that you can get from your wind farms in Oz is one that you don't have to use fossil or nuclear to generate !
This means that you Ozzies get richer as you can sell that fuel to the rest of the world desperate for energy.
With respect to your argument about needing extra generating capacity - whats new about that ?
You have to have extra capacity at present because the amount generated by plants of all types including windfarms have to be matched to a constantly varying demand by users and to cover breakdowns.
Minute by minute electricity demand is met by a mixture of sources at present. baseload ( typically coal or nuke ) stations churning out most of the demand.
faster reacting but less efficient generating plants fill in the gap ( typically gas turbine or pumped hydro storage )
With wind in the energy mix the top up is still needed as demand changes, just the mixture of sources will be different.
In a well sited wind farm the output will change slowly compared with demand and will be predictable from meteorological conditions.