Hi Mathias,
Yes, it can be done. Most of the admin pages have an extra css class named "admin" on the wrapping div.
So you can add this to the bottom of your styletext.css file:
.admin { font-size: 150%; }
Then clear the server cache by touching Web.config, then clear the browser cache, and you will see much larger font in the admin areas.
Most features have additional css classes on the wrapping divs that are not used but could be used to style the feature different from others. Most of the time with skinning we are going for a consitent look and feel across features, but these extra css classes are there to make it easy to customise things differently across features. All you have to do is view the source of the rendered page and studdy the css classes on the divs wrapping the content.
Hope it helps,
Joe