I'd make the questing more savored and challenging than it is in WoW. They made quests more interesting in some places, but nonetheless pitifully easy. it's kind of funny how the two factors combine:

giant dragon: rawrbargle! I kill you!
Garrosh hellscream: I'll help you fight this giant dragon!
me: naw, I got this. *pokes it with a dull stick and it falls over*

heirlooms were an OK idea to make alts easier, but unless some weird guy is making the same class and spec over and over, a slower leveling process with some challenge creates a smooth learning curve so they are somewhat competent by the time they reach the level cap, and feel like they've achieved something.