I went to Galignani a couple days ago and have to say, you're right. The selection is very good--I saw lots of books I'd never seen in person. 2 copies of LPT (but for 100 pounds!) and lots of books that are already on the Alexander Palace. A lot of them were very expensive (at least, to an American. the exchange rate is horrible right now) but I got
Once a Grand Duchess about GD Xenia and am enjoying it very much.
Here's a picture of the store if anyone's going to visit and doesn't know what to look for.
P.S. If someone asks you, along the Rue de Rivoli, if you speak English, just say no.
I heard someone saying their pocket got picked right there when they were drawn into conversation.