If there's a good enough workflow, there's no reason to not use LESS and SASS in each app. You compile the CSS before production anyway, which means you work with beautiful code, and use automatically minified code for production, and all of it is (usually) taken care of in the background.

Plus, if I work in CSS for simple apps and LESS for complex apps, I have to keep two sets of boilerplates. I don't want to be writing CSS from scratch every time I make an app. With using LESS in every instance, not only do I only need one boilerplate, but that boilerplate is modular and I can take the things I need and exclude the things I don't. LESS effectively has namespaces to make this super easy and MORE efficient than plain CSS.

No comment on CoffeeScript, though. I've not had to write enough JS to warrant checking it out in depth.