Doing a leve on Legion difficulty, I got I think ~30% more gil. No better item reward, just more gil. It did equate to more xp, but only because the monsters are higher level (if still only 2-4 hits to kill them). The problem of course being they seem to hit much harder, as well. I died 4 times before I succeeded, whereas I'd never died on a leve before.
In other words, not worth it, really, at least not soloing. If you have even a group of two, hit Legion. You'll succeed on the leves currently available, and get more for it.
Edited, Sep 9th 2010 10:50pm by Kevrlet