Can you look for the award tickets now?

They might be as cheap as 120K for 2 Y tickets, which means you do not nead to purchase any miles.

The next lowest price would come in at 150K, and obviously this purchase would help but not get you there on its own.

In general, only purchase if it is fairly clear you can see how to use them. You are knid of in-between, and one can not give a decent answer w/o knowing what those flights to S S. America will cost in miles. [EDIT: I assumed South S America, not North S America, whcih is a bit cheaper]

And AMEX bonus offers can really be your friend here.