Most of my work in the last 3 years has been on internal tools. It's not quite infra level and its also not quite business level/product focused stuff.
I'm not sure how to quantify impact here.
Here are some thoughts:
The main one is how many employees at your company use those tools, particularly engineers.
Aside from that, it's pretty context specific. If you can share what kind of tools you're working on (build speed, testing, linter), I'm happy to share more specific ideas.