I see this is an old query but there should be an answer for this as it's at the top of Google, better still there should be support for this in game by now!
Go to Origin games directory then SimCity\SimCityUserData\Preferences and open Preferences.prop with notepad
(default directory is C:\Program Files (x86)\Origin Games\SimCity\SimCityUserData\Preferences\Preferences.prop)
Press Cntrl+F and search for OptionUIZoomLevel and change it to 2 or 3. 1=100% 2=200% etc.
Be sure to restart the game.