CX Lounge in MEL
 

why CX set up its own lounge in MEL rather than just accommodating the F/J passengers to the Qantas Club instead? it seems that just placing the F/J passengers to the Qantas Club is more cost effective than setting up its own lounge.
Same case occurs to NRT with the selection between using the JL Sakura Lounge and setting up its own lounge.

The reason is brand positioning. You don't want pax to spend time with another carrier for ANY time. Each airline has a different strategy/rationale for when to develop its own lounge -- depends on the number of full-fare C/F pax and the number of flights. MEL would likely have a lounge for each carrier that has 2 or more daily flights with reasonable numbers of C/F pax. For CX, MEL market is a no-brainer for why to develop/operate its own lounge.

Not really, CX has more flights per day through SYD, and probably more J traffic through SYD too, and they use the QF lounge there.

Maybe they wanted to, but just can't?:D

Perhaps the QF lounges at MEL were just too poor for CX's requirements? Until about 2005 this was certainly true, and CX had a nicer lounge than QF at MEL. Then QF rebuilt the J lounge (and built a new F lounge which is almost Wing quality), so now the QF lounges are significantly nicer than CX at MEL. Floorspace at SYD was much harder to come by, so CX may not have had a choice in opening a lounge there. Now CX service to MEL is reduced (and QF operates a nicer MEL-HKG flight than CX; how times change). Still CX has its own quaint lounge there; probably not what they would do if given the choice.