It really seems like you don't understand how Sass works, or at least haven't actually run it. If anything, Sass layers more gracefully than C does over x86, since compiler-generated x86 is incomprehensible, and Sass-generated CSS is probably more readable than what a typical designer produces. Sass also promotes CSS best practices, in part by automating them, and in part by providing syntactic sugar for them.
If your designers can't grok Sass, you do what every professional team using template languages has always done; you back-and-forth with the designer in CSS/HTML, and you convert final comps to templates. Designers by and large don't speak Haml, Erb, Clearsilver, or Cheetarah (or Mum-raah or whatever Django calls it) either.
The designers produce the CSS, I don't. In most cases, they use their fancy tools to produce it. If they're not using SASS, what's the advantage to me? Why would I convert their CSS to SASS to get the same result in the end?
Templates are a different story -- that's where the design and the functionality meet. I do convert the final comps to templates and if necessary the templates back into static code to repeat the process (rarely necessary, but it happens). This is a necessary evil. Why would I want to perpetuate that evil in CSS as well?
You know what's funny: I know of several design firms that are using sass to generate their css and they deliver the generated CSS to their client without ever telling them that they used sass to make their development process faster.
If they had given you their Sass code, you would be empowered to make design changes much more easily that you could have with CSS. If I were you, I'd be demanding that my designers use it ;-)
If your designers can't grok Sass, you do what every professional team using template languages has always done; you back-and-forth with the designer in CSS/HTML, and you convert final comps to templates. Designers by and large don't speak Haml, Erb, Clearsilver, or Cheetarah (or Mum-raah or whatever Django calls it) either.