to each their own.... I'm still thinking my wife doesn't truely appreciate the number of airports we are going to be visiting on our trip, well, she's stuck with me :P

Just one quick correction - by starting in Z2 to Australia via Japan (or Z8) you actually save miles too - 10k (C+M) on a return flight in economy, multiplied up/down as per class and return/ow. However - for a direct (i.e. not lots of stopovers or a trip via NRT/ICN) flight to Australia you are right, you'd save no miles only APD. As such it is probably less worthwhile in your scenario. APD is also only charged when leaving the UK btw, so, on the return flight it doesn't matter - so your comparison point would be £110 per person (plus a few extra earned miles) for your starting one-way flight. On your way back, as long as booking as two one-ways, you can go all the way back to the UK without paying APD. I suspect in your case it is not worthwhile!

The only other stopover I can think of is ICN (i.e. OZ flights - LH also flies to ICN) - they do direct flights ICN-SYD and from other European hubs (LHR, FRA etc) there. Whether you want to visit S. Korea with their friendly Northern neighbour is another matter. This is also probably not a particularly direct routing, however it is an option.

Unfortunately can't help with 1.

PS If you did want cheap miles then Swiss are doing a nice business class sale into Europe for reasonable fares, but you have to transit via ZRH/GVA so its not that convenient for a lot of places. Think you can safely say you don't need though for just this trip.