I was curious if there's a command line tool for building *.quest games. I didn't see anything at Codeplex or in my Quest install, so If you use a text editor to edit aslx, do you still build the game in the GUI?

As far as I know, you still have to load it into the GUI to publish.

No there is no command line tool. But you can open your aslx in the offline version of Quest and in a text editor simultaneously. If you edit the file in the texteditor, Quest shows a yellow bar that there are changes in the file and a button where you can reload the file. If you use a texteditor like notepad++ this works the other way, too.
Normally I open my game in Quest and start playing. After changing something in the texteditor I just restart the game. When restarting a game, Quest loads the changed aslx file again.