I had a 24 hour stopover in SCL, and found that credit cards (including Amex) could be widely used in stores without any trouble. Can't recall the exact name/branding of the network - maybe Red or something similar? - but apart from exchanging the ~$15 or so of Argentine Pesos to Chilean at the airport before I left EZE, I didn't need to change any more currency.
Siempre Viajando - as another Canadian bank card holder, I agreed with you. >$5CDN for an ATM fee is a joke~
but at least I could use my CCs.