New to USA - Masters vs. Staying with my mentor
Depends on what you expect to get from a master's degree. 

From the sounds of it, your career path certainly isn't going to be dependent on the credentials, but could perhaps be aided by a degree. 

Personally, I could see you getting benefit out of a good Masters on a couple of counts: 


An introduction to where the state of the art lies. Since it sounds like you have an entrepreneurial bent, finding this state of the art could help point you in the direction of problems which have been solved, but not productized... could be a great start for a company. 
Another mentor. Having multiple people to bounce ideas off of is a valuable thing, especially when they have substantially different backgrounds. 
A chance to exercise your grit, away from the perhaps comfortable situation you're in now. A masters will force you outside your comfort zone.
The benefits you list are going to be there for sure; an immersion into American culture and life.


Of course, getting all of this doesn't require a Masters degree. You're already living in the USA, and you can try to stretch your research legs on your own.