I'm thinking of doing this DONE5 route:

Cairo (BA)
London (QF)
Sydney (QF or JAL)
Tokyo (Sri Lankan)
Colombo (Malaysian)
Kuala Lumpur (Cathay)
Hong Kong (Cathay)
New York (AA)
Cancun (AA)
Miami (AA)
Los Angeles (Lan)
Santiago (Lan)
Easter Island (Lan)
Rio de Janeiro (via Santiago = 2 segments)
London (BA)
Cairo

The fare rules say I don't have to terminate in Cairo, I can terminate in another Middle East location. For me, Amman would be preferable. However if I substitute Amman for Cairo at the end of the trip, the price goes up significantly.

Am I missing something? Is it pricing the whole trip with the AMM price rather than the CAI price due to finishing in Amman?

General comments on my itinerary also welcome as are the logistics of actually paying US$24,000-odd for 2 adult+child+infant tickets in Cairo when I live in London.

I think I have it pretty efficient. Every flight except Easter Island -> Rio is a single sector and I actually do want to go to all those destinations. Only thinks I'm thinking of now are deleting something like Miami and adding either Cairns or Vancouver.