15% extra for WT+ is always going to be worth it. As someone mentioned, normally it's like 100% more.
I don't suppose it would be worth using *A in your case, given that most of your travel is to HK/Australia?
I suppose flying Virgin would get you miles with KrisFlyer. I also believe Air New Zealand fly from London to HK. If you intent to use a number of carriers in an alliance then *A is much better in terms of mileage accrual, common luggage policy for status-holders, etc.
P.S. Will your travel be from London to HK _or_ Australia or will it be necessary to travel to Australia with a stop-over in HK?