Man, you're lucky. When I level tank or healer, when above lvl50, I am getting the most pesky difficult dungeons I can. The Aery, The Vault and full spread on the above-60 dungeons as they pop up. I want the low level dungeons! If I'd want the high level dungeons, I'd queue for them!

And yes, if you want high level dungeons, then just queue for them. A dungeon that is about your level gives as much experience as leveling roulette does...past the first time you do it with the bonus, of course. Leveling roulette does speed up the queue though...or at least, it's supposed to. To be honest, I only ever did it with tanks/healers, so I don't know whether it's not more of a bottleneck than the individual dungeons at higher levels.
After all, leveling roulette functions by giving you experience at the end that is about equal to what you lose by being at a lower level dungeon instead of a dungeon your level. So just go to your level dungeon if you want to level and learn the class at once.