Thank you for the suggestion of travel via Sth Africa/USA We would be happy to travel this way but travel insurance costs can be prohibitive when your age is over 70 yrs and have past Heart Surgery. I would love to go that way and go on a Alaskan cruise.
We will probable have a few days in China.
I see that you are based in North Queensland - Cairns?
The oneworld award allows for up to 5 stopovers and 35,000 miles. As long as you stick to the rules you can use it to go almost anywhere on oneworld airlines!
A return business flight from Cairns (or anywhere else on the Aus East Coast) to London will cost 256,000 points in business. However, for a 280,000 point oneworld award you could fly, in business class (as an example):
Cairns - Hong Kong - Beijing on Cathay Pacific (CX) - stopover in Beijing
Beijing - London on British Airways (BA) - stopover in London
London - Phoenix - Anchorage on British Airways/US Airways (US) - stopover in Anchorage (Alaska)
Anchorage - Dallas - Lima - Cuzco on American Airlines (AA)/LAN (LA) - stopover in Cuzco (for Machu Picchu)
Cuzco - Lima - Santiago on LA - stopover in Santiago
Santiago - Sydney - Cairns on Qantas (QF)
Purely as an example, the above itinerary would be a valid oneworld award as it has 5 stopovers and comes in at 34,522 miles. And all for 24,000 more points. The taxes might also be marginally higher but not too much. So if you want to use it to its full potential, then a oneworld award is definitely the way to go!
Finally, a quick tip: Avoiding BA and London Heathrow may reduce the taxes.