I certainly didn’t think so as I used my Paladin for countless hours of gold-making (Paladins are one of the slowest classes in the game). But then I decided to try to make a Fury Warrior with 170% base movement speed. Boy did that make a difference, I run dungeons several times faster than the Paladin, hence making 3 or 4 times more gold per hour.
Dugi’s leveling guide is the leveling addon I’ve always used to level as fast as possible. It will show you where to go and what to do in-game, speeding up the leveling process. This is optional though, as the game already does a pretty good job at showing you where to go at all times. The addon does, however, come with a couple of other nice features and perks.
Good news if you are leveling an alt and you have Draenor Pathfinder so that you can fly in WoD, the next 10 levels will only take a few hours. Personally, I didn’t have this until recently and I went back and got the achievement and I’m glad I did. Now I can level all my future alts fast by just flying and picking up treasures for a couple of hours.