In my experience, the biggest wins in syntax highlighting come from just a few wins: make comments a different color, make strings a different color, and if you've got something like shell where strings can contain embedded variable references, pop those variable references into a different color.

One of the big problems with a lot of the examples here is that, well, I spend most of my time on multimillion line codebases. If you want to pop stuff out to me, showing it in a different color is useless because it's not on the same screen; no, the way you give it to me is a macro that takes me to the next location of the thing of interest. And with a macro that lets me move to points of interest... the use of color is entirely redundant.