What would be the best type of ticket to get for a Sydney/Denver/London/Sydney flight that would allow trips to European centres during the London stay? I need a flexible ticket that would allow changes. How many points do I need? Thanks.
A round the world (RTW) ticket would be your best bet - but from a flexibility point of view, a paid ticket would give more flexibility than points.
You're probably best to fly Sydney/Los Angeles/Denver/Los Angeles/London (as I have just done the reverse trip, visiting Denver in a RTW trip but in reverse to the way you're looking at going). Backtracking to LAX is allowed under the ticket (as it is a major hub from American Airlines) with up to 6 sectors in the USA and 4 sectors in Europe are allowed in the ticket)
See your travel agent, but tickets are probably in the vicinity of $2,200 - $2,400 Economy, $8,499 Business and $12,499 First. Using points - not sure about Economy (150,000??) but Business RTW is 300,000.