I'm not sure I understand why precompiling CSS mixins and inheritance are a good idea. If you can define multiple classes for an element (which can override each other), why bother?
The problem of applying multiple classes to an element arises when the definition of one class expects another css class to be applied to all the same elements because there is an implicit inheritance relationship between them. Keeping inheritance in the stylesheet allows the implementation details of those classes to be kept together instead of leaking out to the html and causing display bugs (which are very hard to unit test).
