Well I saw everything from sci-fi convention attire to tuxedos. It looked like there were alot of young girls there in their prom dresses. Wearing a suit would be nice, and you wouldn't be out of place. If I could do it again, I'd wear some dress pants and a nice buttoned shirt.
Most of the people that were dressed up were bringing dates. Most of the "freaks" were solo or in groups. That could bring up a whole bunch of chicken/egg dialog.
If you don't have a tickete yet, here's some advice. I think the level you sit on is less important than how far left/right you're seated (as long as you're not in the nose bleed section). Since it's one of the few concerts with visuals you'll want a clear, straight-on view. Luckily, we had good seats with nothing to worry about. But there were people with more expensive tickets than us that probably had worse views.