I think the best thing to look at is whether as a US silver or gold you can upgrade on United or alternately, get some US flights and UA flights and credit them to a UA account. I think the best way, maybe the only reasonable way to do this is as a United premier flyer. You are so far from the miles necessary for 2 upgrades that I think you should start over collecting miles credited to a UA account (unless you can do it as a US elite flyer). As a UA elite flyer you can upgrade to Oz on discounted tickets (although not the very cheapest tickets). You will likely have to watch bonuses and do some mileage runs for this. But it will be a lot cheaper than buying the tickets and you will get to visit some other places.