My own competition is famous doctors. Looking at their websites, some go really narrow (like a single illness), and some go amazingly broad. Broad scares me a little bit for myself. It means more research to cover the things I can’t just rattle off the top of my head. I actually do go broader, but I’m always trying to pull back to my core competency.
From that point of view, I think I would draw the line at what you want to be known as the expert for.