I think the 4e magic item price guides (adventurer's vaults) really work for MMORPGs.
However, the idea of craft skills and being able to create a person's own items, that's kinda cool. Like, more to pick up than just gold and items. Meat, ingredients, etc. Also, though, having a 4e chart for stuff that drops on creatures would be cool. I like the treasure packets, but what goes in them... well, it'd be useful to have a reference table.
I like the idea of a world that exists at its own level, not the players' level. I have a setting that is evolving with them, but currently they've had to play smart rather than attack the werewolves in the Thieves' guild; to avoid attacking the level 11 Ogre Warhulk.
Basically, having places that are that level even when the PCs are not, that is kinda cool. Gives a sense that things have continuity.
To that end, I've got my campaign based on the 3 tiers. The local Tier so far is like the one in the DMG (a bit different). The next level, they'll be in my setting's version of Sigil-meets-Asgard (from Thor comics), but they have to unlock that city for their world; which involves quests to various places around the world(s) through portals, dealing with the rise of demon princes and armies of Gith and Giants and Drow who'll be running around the place. After that, they'll be epic; working out the details, but basically more Exarchs walking around (some of them also, I hope), and they'll be fighting Tiamat, Vecna, Orcus and others (Cthulhu, Ilsensine, etc., if I play my cards right), all of this throughout the Cosmos.
However, they'll still be able to go back to, say, Winterhaven or Thunderspire Labyrinth when they have to. Thunderspire might be their seat of power by that point, rather than where they get sold as slaves, but you get what I mean.
Which means I've got ideas for cities in the Underdark, and NPCs of note, and that I've been using those statblocks even now.