Consider this: What if the leveling experience weren't tuned to catapult players so quickly through and past leveling zones and dungeons? What if the pace were a little looser, giving new players more time to soak up the leveling game itself -– and then at the same time, the current XP boosts were spread across tools designed for experienced players who choose to hop, skip, and jump their way to 90?
The precedents are there -- just look at the heirloom armor system. Today, you can buy Grand Commendations to boost various reputations for your characters once you've played through them once. And remember when everyone was buying the Tome of Cold Weather Flight for their alts? The tools are already in place. From leveling XP to reputation gains to player convenience, the helping hand of a level-capped main character is key.
Do you think WoW's leveling experience should remain something to be played through quickly and efficiently, even for brand new players, or do you think there's merit to allowing that part of the game to move at a more deliberate pace? Would you support more mechanics that give experienced players a way to speed up leveling for their alts, preserving a slower pace for new players and players who enjoy slower leveling? If you like a strong emphasis on mechanics like heirlooms and commendations, should those tools be simple, affordable purchases for any level 90 player, or should they take some time, effort, or money to earn?