Another point worth mentioning is that the Cordillera Real is a lot more stable in terms of weather than the bigger, more solitary peaks on the border (Sajama & Parinacota).
We had typical weather in both places when we went during June 2009. The Cordillera Real had blue skies, stable snow and glaciers, warm days and cold nights. We climbed the Cordillera Real in soft shells with a thin base layer and medium weight gloves. Leather boots would have been fine. The weather on Sajama & Parinacota is a totally different story. High winds, extremely cold nights (0 degree bags were fine even at high camp) and lots of evil cold while climbing. We wore gortex jackets with sub-zero MH down jackets underneath, as well as a thick mid layer and a heavy base layer. Even so, my climbing partner had a nalgene freeze on the inside pocket of his sub-zero jacket.. Plastic boots were necessary on Sajama.
I am not saying that you shouldn't bring heavier gear for the Cordillera Real, it is just less likely that you will need it.