I'm doing a quick SYD-MEL flight at the end of the week to pick up a car, and have found that the marked-up prices for economy tickets means that Qantas Business Class is actually better value all up.
However, do I get access to the Business Lounge on a Classic Rewards ticket? Old, old forum posts state that you do, but I don't know whether Qantas have changed their rules in recent months/years.
If you get yourself a Classic Reward ticket in Business Class, then you can use either the regular Qantas Club lounge at Sydney Domestic Airport, or you can use the Domestic Business Lounge. Not sure if you are returning by air, but if you are then Melbourne airport is the same and you can use either the Qantas Club or Domestic Business Lounge.
I had a trip down to Melbourne from Sydney in December 2014 on a Classic Award and was given access. I just had to show my boarding pass.
As Jack said, yes you can - a ticket is a ticket regardless of how you paid for it (points or cash). Use the business lounge... the business lounge in melbourne is actually inside the qantas club, just keep heading towards the back wall