I have heard of as many as 10,000 expats total (not jut US but including Canadian, European, South African, etc.) in Ecuador — up to 50,000 in Panama. I have not done the research on Chile. I think these numbers err on the high side – -especially for Panama and may be some combo of full-time, part-time and tourists at any give time.
Don’t know how you feel about expats — they can totally change the flavor of a place. They can also bring a lot of amenities and services you might want. But remember that 4,000 in a city the size of Cuenca is less than 1%. It doesn’t have a lot of effect except for the expat-driven businesses. If you go to the expat hangouts you’ll be swimming in them. If you don’t, you may not notice they’re there…