My mage team is 65 and hope next week to finally make it to WotLK. I've rode my mount to all the dungeons so far that I wanted to try out and it hasn't been that big of a deal. More time consuming, sure, but it's not that big of a deal.

Once I hit 60 I flew to my dungeons - too cheap to spend money yet for faster flying birds, but once I get to WotLK I think I'll splurge since by the time I get those mages to 85, I'm sure they'll have each earned the 5k gold to buy the mounts.