I'm pretty sure the font size on the tooltips are directly controlled by the resolution in which you play. So, in order to get the font size bigger on these, you will have to play on a smaller resolution (or is it 'bigger'? I can never remember which one it is
-- on the 800x600 end is what I mean).
o O ( I could be wrong, though. It has been known to happen on a
rare occasion
)