Santiago: Turbus transfers is my favourite compromise for getting to and from the airport. Shared mini bus dropping you at your hotel with a fixed price.
I hadn't been to SCL for 2 years last time I went and I reckon it has upped its game somewhat, Bellavista was kicking for beers and wine. Likewise the Bella Artes district is lively, laid back, cool and bookish.
"Boring boring Santiago" also treated us to a drunken street brawl outside our hotel's bedroom window which was a treat to behold. It certainly appealed to me as a Brit.
Providencia around Metro Los Leones where the 4 Points by Sheraton is, is still as dull as dishwater but not unpretty and definitely safe (save for normal city smarts)
No vaccines to enter Chile I don't think (I have arrived from Madrid, Lima and Bogotá) but don't take any food with you, they are fussy and confiscated my pine nuts and porcini mushrooms a couple of years back. Back in 2003 ish there used to be a really funny sign telling you which ham you could enter with.