I've found the social life pretty good at unsw. I'm in commerce too.
Basically in 1st year I recomend you spread ur schedule out, unless you live ages away. If you know people in your course, thats great ur off to a head start. Otherwise best advice I ever got at uni from the guy from my info day, just go up and speak to anyone - people are in the exact same boat as you.
If your into being actively involved there are heaps of societies you can get involved in if you have a particular interest, most people arent into that. I was but i'm greek so like i had a choice.
Library law will me a major hangout in ur first year...then u kinda get shifted all over the uni...people will tell you that roundhouse is all good and that, which it is ---> but if your a lazy commerce student like most of us, you will not want to bother with the treck down to the bottom of the uni. This is stupid but you might be bothered to treck further to the regent for a cheap steak.
Also people have mentioned randwick, maroubra, and coogee you always have people heading down there. Plus quick trip to bondi junction as well if you have a massive break and can be bothered.
Nah uni's a fresh start and if you make the most of it you will have a great time, meet great people, and have great times with the mates you already have from school.
I didn't pick usyd for most of the reasons you said...but fair go im sure people have a good time there too.