HN user
Probably a better idea would be to decide the appropriate content based on various criteria on the server-side. Otherwise the stylesheet will become a nightmare to maintain and would contain a lot of inappropriate logic which doesn't belong to css.
There is already a tool which has all the features you need to help web developers: http://code.google.com/p/wro4j/wiki/Features
It can be used during development, as a runtime or buildtime solution. Also it can be used as a command line tool. It supports almost all known processors (less, sass, coffee, etc) and allows static code analysis with jshint, jslint or csslint.
Would love to hear more feedback regarding usage of scala in big companies with large code-base.