You are already at a reasonably high rate, even compared to the US. That rate is about 250k annualized, which is a good senior developer salary at most companies outside the big tech companies. It is possible to make more consulting, but it would require the hard work of building your US client base. Specialization matters as well. I think you might have trouble finding many projects through agencies, as that rate is higher that most Agency rates I’ve heard quoted, but again it depends on specialization.
So no, there’s no low hanging fruit here. I’m sure you could improve your rate in the US by 2x or 3x by running your own business, but as you are already in a very optimal place there would be hard work involved. And honestly, Americans put longer hours in, pathologically, so you may find the return on investment to work for American clients to be distinctly lacking.