When I upgraded to JDK 7 and Mavericks, this is what JDev looked like for me (just the application browser shown because that's where I wanted the font size to be different). The font looked too big and felt like it was taking up too much screen real estate.
After the change below, it looks better. There is still a fair amount of vertical space being wasted, I could not find a way to fix that, however the smaller font is much easier to work with.
To make this change happen, I opened the Terminal and went to the following location:
The exact number after system11 may be different, depending on the version of JDev installed.
Inside this directory is a file called ide.properties, which I opened and updated with the following:
The Ide.FontSize.Aqua did not seem to be doing what it was intended so I commented it out and put in a catch all font size setting.