So a resounding

on the sleeping at LAX. Bummer. Oh how I wish the lounges were open overnight!
Per UA, since my PHX-LAX flight is on a different PNR from my LAX-EZE flights, I can't check my luggage straight through from PHX to EZE. I have to collect it in LAX and then can't check it in until UA opens up at 4am. (I was very surprised by this - called a few times to double/triple check. How irritating!)

So by the time I'm on the ground w my luggage in LAX, it's 11pm. At hotel and asleep by 12, up at 3:30am to head back to the airport to check my bags at 4am for my 6am flight - it just seems like alot of hassle for 3.5hrs sleep. I appreciate all the input and the dose of reality, even though it wasn't what I was hoping to hear.
The IAD part sounds much more promising

- thanks for all the good tips! I'm looking forward to having some time on the ground there.