Thats not something I've tried.
Theres a suggestion for setting the font via the java command line here:
http://superuser.com/questions/652606/increase-default-font-size-of-java-gui-applications but I dont know if that will work for all of the ZAP dialogs - we explicitly set the font size in many places - thats a hangover from Paros days :(
You can also reduce your screen resolution, although thats a pretty drastic step.
I had to do that on my Windows 8 laptop as loads of programs came up way too small ;)