I have to agree wholeheartedly with this. SASS gives you access to loops and true logical computations (if/else etc). I’ve found these to be invaluable in creating things like on-demand grids which as far as I can see just wouldn’t be possible with this.
I believe that computational logic such as calculation of dimensions based on variables is slated for future inclusion, but SASS gives me that capability now and without the need to worry about whether the syntax is going to change suddenly in a month.
As far as the arguments against having to learn a “new language”… I would argue that anyone working on any remotely enterprise-scale websites or webapps would probably already have at least some exposure to preprocessors - There’s just too much time saved by using them for dev teams working on projects of that kind of scale to ignore. They not only make the initial code faster to write, but increase maintainability as well.