Hmm that's interesting -- you can overide image sizes and other stuff in the "Node overides" tab of the menu, but you can't override the font size.
Does seem like it might be a nice idea though.. Let me put it on my todo list and see if i can implement it easily.
At the very least it seems like i should be able to provide a way to specify two fonts(+sizes), one for root level of dock bar and one for the submenu items, etc.