I would find it useful/interesting if I could get some kind of historical value tracking of my collection. Currently I am doing this outside of Deckbox periodically but a built-in automated implementation would be handy.

EDIT
Also it would be great if you could see your top 'movers' for the week/month similar with what MTGgoldfish does but only with the cards in your collection.

I second this, would work for decks as well.

Would definitely be cool, although for various reasons it's not trivial. Pricing is still not in the position where I'd like it to be...