"The book even goes on about how death was designed to be a whole other feature of the game, and that while dead you could see new sights and even special ghost monsters that guarded important locations."

Hmmm. Well, there's Franclorn Forgewright, the ghost who gives you the quest for the BRD key, who you can only talk to while you're a ghost yourself. And there's some quest or other that requires you to drink a potion in the Gadgetzan graveyard, at which point you die, and your ghost has to talk to a ghost in the hills just north of you for the next quest in the chain. I can't think of anything else though.

@Cyrus: There's a questline in Grizzly Hills to save a troll city where the dead are being held captive as ghosts, so you have to die to talk to them.

They sadly STILL SELL the 2nd edition strategy guide everywhere. It's so old, it doesn't even have Naxx 40 in it yet. I flip through it from time to time for nostalgia's sake, but then facepalm when they still have the audacity to charge $25 for it.