If you really want to see the andes, with lots of volcanos included, you should think about spending a day or two in southern Chile. From Santiago to Temuco it is about a 45 min flight. They are not too expensive, with many daily departures. Around Temuco, you can reach the conguillio national park and the Llaima volcano in about 2 hours. Within about 1 hour, Villarrica lake, the national park, and the Volcano.
Crossing through Bariloche Argentina via Puerto Varas and Ensenada is much more attractive than Santiago- Mendoza. One of the cooler crossings, is to take a boat across lago de todos los santos (right on the boarder), and get on a bus on the arginetina side to finish your trip. The Santaigo-Mendoza crossing is more less just rocks or snow (depending on the time of year), and the mountain is just one of million mountains in this part of the world. Nothing you would want to email around to the family.
If you do the Santiago to Mendoza trip, it is better to take a bus through the crossing. The Chilean-Argentinian border, "Paso Los Libertadores". Buses in Chile are first class, comfortable, clean, and very cheap. The road is mostly switch backs (something like 100 or more), and better to let the drivers that do it everyday handle them. The best is turbus. You can check prices and schedulle on their site at: http://www.turbus.com/html/noti_taschoapainter.html
Santiago and Mendoza, being just big cities, probably will add little to nothing to your Latin America trip. Mendoza is mostly a shopping mall for Chilean's to visit on the weekends. Nice place, but mostly a place designed for shopping, lunch or dinner, and then get on the bus back to Santiago. Bariloche, in the south really looks more like aspen Colorado overlooking a lake with ski resorts, yet still has a fair amount of places to shop.
For flights inside Chile, www.lan.com
More info on the south, our site, www.allsouthernchile.com
Any information you might need about Chile, Mendoza or Peru, please feel free to contact us. We have done all of these at some point.
Charles and Zandra
editor @ allsouthernchile.com