Which terminal?
I have very fond memories of Hermes scarves, Chanel costume jewelry, and similar goodies at Terminal 1 many years ago, but the last two times I was there shopping was very limited due to construction; probably it's completed by now. I thought the selections at Terminal 2 (and I've checked as many of the sections as I could get to from the AA area airside) were very disappointing, perhaps because so many of the flights there are to the EU, for which duty-free prices don't apply.
I think it's generally true that onboard DFS prices are slightly cheaper than in the airport, if they are carrying the item you want. And given the dollar's decline against the euro, you might still do better in the US nowadays.