I've worked as a principal engineer at Amazon before, and I can tell that testing and quality there isn't looked down upon. You can definitely get promoted just for improving products and never building any new feature.

However it will matter a lot on where you spend your effort on, and whether your environment understands why it matters. If you just mention "I'm writing integration tests" - and nobody knows why it's important to do that right now - it will likely not go too far. However if it's along "we have this regular operational issue that everyone in my org including the director was aware about, I fixed it, added integration tests, and made sure I added automation that will catch further regressions before our customers will observe them" - it will go a long way.