How to slow down leveling

My wife is a casual World of Warcraft player. She doesn't participate in any form of group content, neither dungeons, nor raids, nor PvP. In consequence there isn't much to do for her in the "endgame" besides daily quests, and thus she has tons of alts and spends most of her time leveling. And since Cataclysm, she isn't all that happy about her leveling speed: It goes too fast.

The problem is a design philosophy of Blizzard, who apparently decided to keep the overall leveling time up to the level cap more or less constant. So every time they add levels on top of the game, they need to make the lower levels faster by the same amount of time. Three expansions after vanilla this has led to downright silly leveling speed under 60. Thus if you are a casual player, and want to play through the quests of a zone, it is kind of annoying if you outlevel the quests before finishing them.

Thus me and my wife worked out how we could slow down her leveling speed to a more pleasurable pace. Now the first point would be to remove heirloom items that give xp bonuses, but my wife hasn't got any of those. The second strategy is deliberately logging off outside of cities and inns, so as to get less rest xp bonus. But ultimately the only thing that really works well is paying 10 gold to stop all xp gain. There is an NPC in the main city's PvP building which allows that. Stop gaining xp, play until the level of the quests and mobs rises higher than yours, then turn on xp gain again for another 10 gold.

This works, but in the end I still think that Blizzard has a design problem here. The needs of the players who think that the game begins at the level cap, and who want to level as fast as possible, clash with the needs of the casual players who want to have fun while questing and leveling. Leveling from 1 to 60 feels like watching a movie in fast forward, not a good speed if you are actually interested in enjoying the content. Sometimes I think it would be better to slow down leveling back to vanilla WoW speed, and simply sell people level 85 characters with BiS blue gear from normal dungeons for $20 if they desire to skip the leveling part.