That's good to hear about the time conflicts thing, I've never attended an actual festival before, but it seems like you sometimes have to make some really hard decisions. I would go to this for The Lawrence Arms alone, mostly because I still haven't seen them yet, haha. Pretty much everyone else that interests me I've seen at least once, it would be cool to see Rancid again, but I'd like to see them in a more intimate setting.
I've seen most of the bands I want to see before, but some I haven't seen for quite a few years (Millencolin, H2O, the Lawrence Arms). Honestly, though, the appeal for me is mostly to see bands in a setting outside of the way I normally see them (i.e., a club or theater gig). I like to see how different bands handle crowds, set lists, etc. There's also the element of "bands I'd watch but would never pay $40+ to see headline" at a festival like this (Marilyn Manson, Anthrax) so...I dunno. I'm a dork.
The year I went, it was basically punk/metal band alternating on the main stage, and it looks to be the same this year. Though, I'll say that going from the Offspring to Marilyn Manson or from Alice Cooper to Rise Against won't be anywhere near as jarring as Lamb of God playing after the Descendents. Haha.