"Obviously there's a diminishing return if you hit specialization of 'There's one business in my region I can market to' -- how do you know when you've specialized enough"
Iterate. Too many companies come out? Become a
little more specialized, based on your research. Too few? Become a
little less specialized ("SEO optimization for women's fashion and
beauty stores selling $1,000,000/yr and based in New York" →
potentially too specialized)