Nice work on this library installer!
You might like to know about a similar effort I've been undertaking for the last year or so... to test and port all "major" Arduino libraries to Teensy (which is 3rd party board my company makes).
Here is the list of all the libraries.
http://www.pjrc.com/teensy/td_libs.html
As you can see, I still have quite a number of them to test. Usually when I add one to this list, I buy the necessary hardware - but often it sits for weeks or months due to lack of available time.
A few months ago, I added a feature to the Teensyduino installer (which automatically adds the Teensy-specific files to Arduino) to optionally install any of the tested libraries. Virtually all the libraries are only a few relatively small files. Just copying them all into installer didn't enlarge it very much, less than 1 megabyte.
Several times I considered making a java-based tool right inside the IDE - which does pretty much the same thing your nice-looking application does. The really hard part, though, is the last of a central database of all the libraries. Maybe my efforts can help, at least a bit, or I might be able to contribute in some way?