I would slit my wrists before spending a minute more than absolutely necessary in LAS.
I second the recommend to head to the Air & Space site at IAD (8 min cab ride?), if you've got the time. It's incredible what they've got assembled there (an SR-71, Concorde, Space Shuttle, Enola Gay, etc.).
I'm sure it will draw a few guffaws, but I think that ATL has a lot of really interesting (and rotating) displays, even if it's easy to miss them. JFK is a hole, but it's still one of the world's crossroads. Can't beat the people watching in that.