I tried turning off display names, but I wasn't quite the biggest fan of it. I tend to wave at people I know when I run by them, so without it on I'd never be able to know who's who. I may try it again, but for now I'm fine with them still on.

That said, what I have turned off is the mini-map and exp bar, and moved the Duty List to where the mini-map used to be, and it greatly reduced screen clutter. To be honest, there's very little point in using the mini-map, even for gathering since all of the nodes are often close by, and any enemies you're fighting are probably up in your face anyway. And there's also really no need for the exp bar, either, because you can check your exp totals on the Character screen. It's amazing just how much screen space is saved when you remove those two, and I hardly notice those two element's absence.