Hi Fitz!
thanks for the post and the compliments

Have you read the Aconcagua trip report on this site?
Check it out; we were very happy we brought a down jacket (both of us had the The North Face Baltoro jacket). When you are climbing it's not needed, but when sitting at camp, cooking or just wandering around without a pack it's very useful as it can become really cold.
As you can read I checked the temperature while melting water in camp II and it was -25 Celsius/ -10F and it wasn't even dark then and there was no wind...
Also the guy we rescued on the way down from the summit was wearing a down jacket to the summit; if he hadn't he might have frozen already

So if you can afford it, buy a down jacket. For the climbs, bring a Goretex, something you can trust in very severe winds, and where you can wear some fleeces underneath.
There is little rain to be expected on the mountain (maybe on the walk in), but lots of wind and probably snow.
Hope this helps,
good luck on Aconcagua,
Thanks and keep climbing,
Harry
ps: don't forget your feet: every year too many people get frostbitten as they take only leather boots