I 80% agree with this, but I've also gotten a lot of mileage out of Emacs hi-lock mode. The simplest thing I always want: whatever symbol I'm pointing at right now, highlight everywhere (so I can trace it through the code quickly); more generally, I want to highlight an arbitrary regex, so for instance when I'm auditing a codebase for authorization, I quickly spot the functions that aren't following the same authorization patterns as all the others.