The store is amazing -- many guides recommend it as well and their entries are full of details so... what can I add?
My claim to fame is I went through the place twice with two spoiled little girls and only spent $20. How?
First I went only on Saturdays (two in a row). The girls were delighted just to be on the same block as the store (believe it or not) and the velvet rope/doorman out front was worth ten minutes of picture taking both times we went.
Inside, the place was packed wall to wall with moms and dads carrying boxes bigger than their children, we could hardly hear each other speak let alone get close to the merchandise. The girls enjoyed the crowds and the glamour of the place (yes, doorman + the aforementioned velvet rope + 8 years old = glamour) and I tried to make them think of the place as a museum of dolls rather than a store where we could actually buy things.
Secondly, each time we were there I tried to spend as much time as possible on the first (below ground level) floor. There are cases containing each doll and every bit of the dolls accompanying stuff - desks, beds, outfits, etc, plus little cards that describe the item along with its price. We collected each of the little cards and played American Girl 'Go Fish' with them at the hotel later. We took catalogs back to the hotel too for making wish lists.
Finally, there was a book signing the second time we were there, happens often I understand. The girls were completely thrilled to get an American Girl book signed by the author (extra thrill for the girls - she was in period costume), and the author was kind enough to chat them up for close to half an hour since no one else was buying books.
Next time I take them I've promised one thing -- they can bring their dolls to the hair salon. Yes, there is a full service hair salon complete with tiny chairs, curlers, wee pink robes and real human stylists. There are about a dozen different hairstyle options and of course there is a charge for the new hairdo. A ridiculous waste of money and yet I found it oddly irresistible.