Using SoapUI v 3.6.1 on Windows 7 and the text is tiny. Didn't find an option to increase text.
Select File > Preferences (or hit Ctrl + Alt + P) from menu and then pick Editor Settings group. Hit Select Font... next to Edtor Font and choose a different size/font face.
Hit OK to confirm your changes. Any already opened editor window must be closed and then reopened in order to above mentioned changes to be applied.