The aircraft is meant to increase density on a given route. Fly more pax there with less metal. The point would be to send it to LHR and replace a couple of 777 rotation, or simply increase the seat offering on that route without the need for more frequency or slots. It is a given that it wouldn't be bought without a careful study of the loads, CX isn't and cannot be a 'build it and they will come' airline like EK.
Yes, it costs more to purchase/finance and operate. That's because it is bigger and thus able to generate more revenue... Business 101. The question is whether that extra revenue can be tapped in CX's case.
Note, however, that the costs of crewing the aircraft is fairly similar to that of a jumbo or a 777, the only difference being the few extra girls in the back. Except you now have 500 pax to share the price of one set of crew instead of 300.
Given they can find 3 or 4 daily long haul trips to send them on, there might not be a necessity to have them sit on the ground or MNL turnarounds, given careful planning. Then again a few regional trips would be needed for crew training, just like with the 744 in its heydays.
Note that our competitors in the area, who have all bought it (in obvious delusion, some will say), seem to do rather well on regional routes. No doubt the 9th floor dwellers will have noticed some big Singapore, Korean, Malaysia and Thai tailfins wading around under their windows.
Simulator costs depends on the size of the fleet. After a certain number of crews is needed, then the cost is just the same as buying a sim for additional 777s, slightly less even since the point is to use less crew for a similar amount of ASK. If the fleet is too small, then it might be better to outsource training. I'm sure QF or BA would be happy to oblige.
The maintenance might be the only major extra cost involved, in terms of training, tooling and parts, but then I presume HAECO and TAECO will be wanting to get on nicknames bases with the bird anyway since they are becoming quite popular in the area.
Then there is the
PR factor. The A380, thanks to Airbus' mediatic tapage, has become quite famous amongst the otherwise unknowledgeable flying masses. Now, CX is not one for one-upmanship, but I believe our customer base is very much one that wants the best, biggest, newest and shiniest. A quick look around HK says a lot that way.
My limited(/quasi-inexistant) knowledge and experience tells me there is room for the A380 (or 748i for that matter) in CX, but it all comes down to vision and risk appetite, none of which I believe CX management and owner possess a lot of.