Here's the thing - you simply don't always get a cheaper fare with a low cost carrier.
Try walking up to a jet star counter in the morning and asking how much it will cost for a ticket in the afternoon. Chances are it will be dearer than the Qantas ticket.
Possibly true, and it always pays to shop around, but I think you'll find thats a bit of a steep generalisation. Furthermore you will never see any LCC offering every seat at rock bottom discounts. It'd fall over in a week. The nature of airline economics is there needs to be the higher fares on board to compensate for the lower ones. This applies to an LCC as much as any full-service carrier.
And just as an example for this coming Monday at similar times:
MEL-HBA: JQ $79 @ 0645, QF $222 @ 0835
SYD-CNS: JQ $299 @ 0705, QF $332 @ 0805
OOL-SYD: JQ $159 @ 1200, QF $391 @ 1215
NTL-BNE: JQ $89 @ 1705, QF $189 @ 1615
At the end of the day its all marketing. By spinning off JQ, QF has been able to successfully increase its yield by pitching itself as the sole full service carrier in the country, and charging accordingly. For QF the cream, jam and whole bloody scone is the Cityflier operation. This leaves JQ to make a buck out of the rest, in markets that QF arguably didn't ever make a profit in.
And on the club ...
QF Club numbers shouldn't really change anyway. Members can still (and do, let me assure you) use it when flying JQ. Maybe it's standing room only over at T2
... or even worse they're all in "The Lounge"
