I have found my thread at last!
I too aspire to dress like UES socialite. Right now my current style inspiration is the fictional Blair Waldorf, from tv's Gossip Girl, but long time favorites include: Jacqueline Onassis, Princess Grace of Monaco, Princess Diana, Audrey Hepburn, Ginger Rogers.
Upgrading my wardrobe has been both difficult and easy. I loathe trendy items and love/own super simple block colour clothes (although I have started embracing some prints) but I don't own enough dressy casual clothes (ie: I own more jeans than pencil skirts, etc). Also, it's difficult because so many of the people I know are into the hipster style and trendy clothing and think I overreact when I tell them something doesn't fit my style.
I do agree with the comments that having a love and support of fine arts, quality food and wine, and education do go along with the style.