To clarify: You can earn Status Credits on these flights if you're part of Points Club. There is currently no way to earn Qantas Points on Classic Rewards flights.
In other words, the only real benefit of Points Club when it comes to classic awards is that you can earn some status credits which is the currency Qantas uses to determine what frequent flyer status you earn with them (i.e. it's not used for making reward bookings). If you are looking to earn Silver, Gold, Platinum or Platinum One status with Qantas and you make quite a few classic award bookings, then yes this could be a useful benefit. You can find the number of status credits you can earn towards Qantas Frequent Flyer
status here. On a business class award from say Sydney to Melbourne you would stand to earn 18 status credits each-way whereas a long haul Sydney to Perth in business class would earn 38 status credits each way. Flying Sydney to LA in a business classic award would earn you 72 status credits each way.
To earn Qantas Frequent Flyer Silver status (which gives you priority check-in, a couple lounge passes and advanced access to Qantas classic award seats) you would need to earn 300 status credits within a year. For the coveted Gold status (which provides lounge access at Qantas and across the OneWorld network, better access to awards, etc.) you would need to earn 700 status credits per year. Platinum which comes with access to such things as First Class lounges and the ability to request classic awards to be made available to you, you would need to earn 1400 status credits in a year. Lastly, for top tier Qantas Platinum One which provides priority customer service you would need to earn 3,600 status credits in a year of which 2,700 would have to come from Qantas marketed flights.
The easiest way to earn a ton of points to qualify for Points Club membership would be applying for a Qantas credit card that has a healthy sign up bonus. For instance, several credit cards available today offer a sign up bonus of 100,000 Qantas Points which would very quickly get you to the 130,000 Qantas Points you need to earn Points club status. One thing to keep in mind is when your program year ends with Qantas. For instance, mine ends this month meaning that any activity generated on December 1 wouldn't count towards the current program year but to next program year. Keep in mind too that there is some lead time (i.e. days perhaps weeks) between you qualifying for the bonus points and them landing in your Qantas account. You would want those points to land before your program year ends.
-RooFlyer88