Indeed, but that only works at certain category hotels (and even then it's not always available). The OP wants to go to Argentina, Chile, and Peru (but hasn't yet explained where in each of those countries).

In Argentina, a small number of SPG points can go a long way at Sheraton Salta because cash+points is available there and a fantastic value. But there's no cash+points at Sheraton Iguazu Falls Resort, and it's mighty expensive on points too (12000 to 16000 points a night, depending on season), so it can drain an SPG signup bonus in no time at all. (I stayed there multiple nights -- during the 16000 points/night season -- using free night certs earn during a promo last summer. I couldn't have afforded it any other way.)