This article by Ilya Lichtenstein proposes a method for competing against bigger, better-funded companies:
- You can learn from their experimentations what works best in terms of marketing message, demographics, etc, which saves you from having to run your own expensive A/B tests.
- You can find the keywords which they're not managing well and target those.
It's worth pointing out that this is an evolving pattern. Five years ago, most companies had no clue about SEO/SEM. These days, they will hire competent firms to do this for them, and so the result will be a lot of money spent on optimising ads, often with some skill.
As a smaller competitor, you need all the help you can get. Learning from your larger competitors is a no-brainer.