STC rating, or as you point out maybe a more expansive take on noise attenuation, is going to be high on my requirements list next time I look at an apartment. I think that and general sanitation (i.e lack of rats, roaches, bedbugs, mold) are the things that have the most acute effect on livability. And not having to walk on tiptoes is nice too. Unfortunately new construction is all about making a building cheaply, but soundproofing is almost impossible to do after the fact unless you want to gut a place.