A language that uses lots of parens to delimit expressions is incredibly bad UX, especially when you try to balance a complex expression, but hopefully there are tools like Paredit to deal with that, so that I can write my Emacs Lisp with pleasure about every day. Similarly, any decent editor will help you out with using correct indentation with Makefiles.

Last modification date is not always a correct heuristic to use, but it's quite cheap compared to hashing things all the time.

Make is a tool for transforming files. I wonder how it's not quite natural and correct for it to assume it's working with files?