Great post, Vailence!
I have absolutely leveled up a new race/class combination purely with the intention of experiencing new content. When Cataclysm premiered, I was eager to not only view the new opening cinematics for each race, but I was especially eager to check out the new quests and leveling experiences that became available when the world as we knew it was torn asunder.
In addition to playing through both the worgen and goblin areas multiple times, I also enjoyed trying out some of the new race/class combinations that became available, such as the tauren paladin. I've leveled up quite a number of characters over the years, so it was really refreshing to be able to have so much new and exciting story content to go through. I found that I particularly enjoyed taking my time to check out and complete the quest chains in each zone before moving on to the next one. Thankfully, since I had so many fresh alts to choose from, I didn't have a problem hitting most of the quest hubs scattered around Azeroth over the passing months.
Leveling new alts has continued to be a lot of fun for me, and it's rather neat being able to take a second-look at pieces of gear in terms of future Transmogrification potential. That sort of thing certainly didn't pass through my mind when I played through some of those quests and evaluated their rewards originally!