As Garlyle said, many high level players would deliberately avoid the roulette for those reasons, and also you might find that new players would not have experienced players around to show them the ropes. Not to mention, several classes are quite dull to play at lower levels -- tanks in particular -- so you would find those players avoiding the dungeons if not for the newbies.

Given they announced recently of looking into the bloat of High Level roulette, they may still do something about Low Level too. But I hope it won't be something like this because to be honest players still learn things post-50 and separating the queues like that would only make things worse for both sides.