What I liked most about these books is that they made you think outside the box about your class. A warrior wasn't just a guy with a sword and a lot of armor proficiency; he could be a swashbuckler of the high seas or a graceful, dancing dervish. Both classes were warriors, but they fought in distinctively different ways.
So when it comes to WoW and transmogrification, I think a lot about the possible archetypes certain classes could have and try to explore those in different outfits. Leather wearers, for example, don't always have to look like members of the Defias Brotherhood or the audience at a Grateful Dead concert. They could also be mud-splattered bandits, solitary rangers from the Hinterlands, or sneaky Warsong scouts. Oddly enough, today's outfit might just work for all three.