I suppose the real question is how superior the domestic business class lounge is versus the Qantas club. Certainly for some airports (I'm looking at you ADL, HBA, CNS) there is no distinction - there's just one lounge area. However, in major ports like SYD, MEL, BNE and PER there are two lounges and there can be a noticeable difference. For instance the MEL and BNE J lounges have nicer views of the tarmac. In terms of facilities they are roughly the same although I think the food offering is a notch better on the business lounge. The one thing where I think the business lounge can make a difference is the issue of crowding. IIRC, the size of most Qantas Clubs and Qantas Business lounges are roughly the same across the network, but remember the only people who can access the lounges are Qantas Platinum/Platinum Ones/OneWorld Emeralds or those flying Qantas business class. The Qantas Club, on the other hand is open to those holding Qantas club memberships, lowly Qantas Gold members like yours truly, those holding credit cards that offer annual Qantas club passes, etc.
-RooFlyer88