The thing I liked most about boxed sets was the ability to include multiple smaller items -- especially maps, but also things like the ship cards from Spelljammer, or the world element cards from Time of the Dragon. That said, I don't miss having the book portions of boxed sets split into pieces -- I really like having all of that material in one package.
For me, poster maps have always played a large role in my campaigns. Having the FRCS hardcover come with a macro-map, and then putting out a four-piece version on a more useful scale in Dragon works just fine, though.
Here's hoping they go that route with Eberron.
As beautiful as the mini-maps in the book are (and it's clear to me that they went out of their way to make them useful, unlike in the FRCS), I'd really like to have a poster map or two to go along with them.
Edit: Oooh, I almost forgot the nostalgia element -- I thoroughly enjoyed being able to put my own campaign material in the box with the other stuff, close it, and take it to the next session. That was neat.