Thanks to everyone for all the help. We ended up booking this with OneWorld since we want to go on beyond SCL and Lan can take us there. We transferred Starwood points to AA and got two off peak DFW-SCL-PMC awards for 40k miles each, a pretty good deal. Since it's around Thanksgiving, we had to buy the BOS-DFW legs but I'm hoping for a bump there...

Again, thanks for all the help and useful info,

Michael