(1) I've been to Chile no less than 30 times, and my limited experience is that you cannot pay in local currency and receive the IVA exemption ... or at least most hotels won't permit it, no matter where you're from.
(2) I like the Four Points location. It is very convenient to lots of things, including the Metro. It is perfectly acceptable, clean and safe, and in reasonably good condition. The neighborhood also isn't as precious as where the W, Intercontinental, etc. is, although it isn't that far. It is also a very short walk to one of my mandatory eats on trips there, a Lomito (or Gran Lomito if super hungry) at Lomit's on Av. Providencia. If you're alone, it is a good place to eat because they have a counter to sit at inside. If you are unfamiliar with the quantities of mayonnaise that Chilenos use, order your food w/o the mayo unless you're sure you really really love your mayo.