You can already do things like this with stylus (http://learnboost.github.com/stylus/). As far as I can see, if you are thinking at this level with css you should be using a preprocessor for sure. I can't remember the last project I used vanilla css in.
Here's a totally silly example, but you can see the power:
color-if-hidden(color)
if @display == none
color: color
.hello
display: none
color-if-hidden(red)
Here's a totally silly example, but you can see the power: