Crossing the Andes is almost a must in your lifetime, and I tell you this not just because I live half the time in Mendoza. Anyone who has done the overland Highway between Mendoza and Los Andes (a town in Chile), will attest on how magnificent and beautiful the road and scenery are; there are also several roadside attractions along the way, including some small ski resorts. Do it someday, you won't regret it!
The road itself does remain open even in the dead of winter, but unfortunately the risk of snow closures is almost weekly, so if time is not eternally disposable to you, I won't recomend it for this particular trip.
I don't think there is any problem with an Iguazu-Buenos Aires-Malargue/San Rafael route, the only variable I'm not sure of is scheduling. Besides that, it's just like any domestic flight experience in any normal country. Since it's a 3 hour drive from Mendoza on 40 southbound to San Rafael, about 4 1/2 hours to Malargue, and 6-7 hours to Las Lenas, I can't tell you what the Malargue 'airport' is like, because I've never been there.
It's probably not much more than a runway with an arrival structure attatched to it. San Rafael is very modest, I did stop there on a flight once, but quite frankly it probably serves it's limited flight services. Mendoza is an international airport, despite my gripes about having TWO jetways gathering dust due to 'lack of planning'... but it's out of the way. Las Lenas is in southern Mendoza, the capital city is in the north of the province (if you had time I would recomend you visit the city).
The Road to Las Lenas itself from Malargue is in excellent condition. Really, Las Lenas has become an international trendsetter and hangout for skiiers the world over, I think you will be quite pleased with the place. IT IS
NOT a city like Bariloche or a town like Aspen where people really live, though. Las Lenas is a resort, where the skiing is as good or better.. but I'm sure you already knew that.
There are other far more qualified 'in the know' about operations of the domestic aviation market that can definately answer your specific questions.
If you have any specific questions about the region, I'm pretty sure I can answer them. Have fun skiing and bring warm clothes, this time of year it's cold everywhere in Argentina, not just up in the mountains!
(except probably in Iguazu itself...)