I just don't understand why they can't do a quick pass and just add a difficulty level to legacy dungeons: hard or easy. It is just a numbers adjustment really. Create a template for each class. Make it so the stat numbers on the template would make the dungeon challenging. If you pick "hard" mode, the dungeon doesn't use your actual stats, it uses the templates... I know it is more complex than that, but it really doesn't seem like such a big deal to do.
As for the op, you need to find a group of players that also want challenging low level dungeons. Find four other players willing to run dm in "white" gear. It blizz was smart they would make an achievement with a mount and title if everyone in the group runs all the old dungeons, at level and in white gear. Maybe the title could be putting "Ford" at the end of your name. I was thinking the title could be "Whitey," but I figured I would get bashed by the SJW's for racism....... Or Blizz could make it an event or a weekly thing- like the skirmishes and timewalking.
Most players just want to run through the leveling process. They probably have a million toons and have done it a million times. They don't want a challenge, they are just trying to run to max level.