Stunning coin!
Regarding value, it is virtually impossible to be precise as these coins are rarely sold and market conditions for Australian rarities (such as pre-decimal proofs) have changed radically in the last decade.
Two major Australian numismatic firms (John Pettit Rare Banknotes and Rare Coin Co.) went into liquidation between 2012 and 2013. Both companies had rather unique business models where they offered a buy-back guarantee of sorts on the coins and banknotes they sold. These guarantees helped attract quite a large client base of not only collectors, but also investors. For various reasons - legal battles, global financial crisis, superannuation fund changes, insufficient record keeping - these firms eventually found themselves unable to honour the guarantees. In the case of Rare Coin Co., there are articles citing the company's guarantee commitments amounted to some A$250 million in client-owned stock at the time of liquidation.
With the liquidation of both firms, and the loss of their clients, there was retraction in the value of many Australian rarities. Take for instance the 1934 proof set sold by Heritage in 2010 for $276,000 compared to the set sold in 2015 for $105,750! As such, I would only consider auction results of the last few years to provide any real indication of present value.