Why does my Arduino IDE hang/crash so often?
Just report it to Arduino.

You don't really have any other option. I've been waiting to answer this question until I was sure that no one here knew the answer. You don't really have any other option.

This seems like a bug. We're not Arduino developers or a bug tracking site. We can only do so much here. Even if it was confirmed a bug and we fixed it, there's only so much that can be done without submitting a report.



BEFORE YOU SUBMIT A REPORT:


I'd try copying out the libraries from Arduino. So many libraries
might make Arduino IDE somewhat heavier. I don't know if it'll really
affect the sluggishness but it's worth a shot.
The only other thing that I can think of, besides RAM (which you
already said wasn't an issue) and the libraries, is some sort of
cache/temporary file. Try reinstalling Arduino, even if you haven't,
and also I'd try using the beta 1.5.6-r2
version. It has to be pretty
stable for it to be the only version that supports the YUN and DUE.
Both have been out for a considerable amount of time with this
software, so I'd imagine that it's pretty stable minus a few issues.



  Many things are said to have been improved compared to the previous 1.0.5-r2 version.


It'd be stupid not to try the newer version.