I'm leveling a Warrior over in NA. It feels a seriously under-powered compared to my Gunner over on Euro and they are about the same level; but that may just be my experience with the Gunner. Anyhow I find that just when I get the Warrior up to the point she feels useful on a Dungeon Run, and I'm really contributing to the run; She bumps up a level and that Dungeon is no longer available for Vanguard Quests. Which leaves me just lame in the next tier Dungeon.
So I was going to suggest just raising the level cap on the Vanguard Leveling Dungeons a level or two when that does not cross equipment tiers. After all people are learning a class in these dungeons, and sometimes thats not always so easy. Harms no one and expands the pool of available players for any given quest.