well,
- on my gnome desktop right now, I go to applications-settings-gnome controls center-font, and there I can choose application font, desktop font, window title font and terminal font
- other programs let you select its own program font
- as gnome-themes, I can also see some liek 'large text and icons',
- in firefox - preferences you can also select font for different text placements,
I think it's doable, but I agree that maybe a general setting to just zoom everything would make things easier