in a nutshell, the appreciating AUD will do 2 things -
1. make the initial capex in AUD less expensive, and
2. reduce the revenue line on the P&L.
2 will reduce the NPV by a far greater amount than the reduction in the initial capex.
To me this should not be a reason to change your sentiment towards SDL long term, it does however reduce the maximum potential of SDL SP by an amount.