It sounds like you are already doing what you want to be doing (startups). Also, your skills are "soft skills" and you already have them and clearly can use them in a practical setting.

I'm not sure what you'd gain from grad school, except connections if you attend, e.g., Stanford business school. I doubt an MBA would improve your technical ability. Is it a dream of yours to go? Is your current startup making money? How invested are you in the current startup?

YMMV: I went to grad school for a technical degree and enjoyed it, but I wasn't doing anything majorly compelling beforehand. My one regret is that I didn't start a startup with all the time I had while at grad school. I'm correcting that error now, but it's a significant disruption of my life.