i don't buy dlc for more quests and items, unless, it's a great bargain. for example, fallout 3's broken steel added actual meaningful gameplay elements and a was a great addition. i have never bought any mass effect dlc. knights of the nine was free on goty. another story isn't worth the money, for me. i would have bought shivering isles, but, again it was free on goty. dawnguard is something i'll buy (unless i wait for the inevitable goty) because it adds actual, new gameplay mechanics.
and, so i'd love to see a "hardcore" mode with numerous, meaningful gameplay mechanics in a dlc. new perk trees and a reworking of certain skills would be nice. attributes and racial distinctions, factions, weather effects, no auto-regen, in-game journal we can write in, added combat maneuvers, degradations, potions over time, reworked trade skills, spellmaking, creating own town/faction, added strategy elements, proper functioning hud/settings options, etc.
i'd pay money for all of that, even though, it should already be in skyrim.