"There's two things you get from a formal education: one is broad, you're exposed to a variety of subject matter that you're unlikely to encounter as an autodidact;"

As someone who has a Ph.D., I have to disagree here. Most of my own breadth of knowledge has come from pursuing topics on my own initiative outside of the classroom, simply because they interested me or because they seemed likely to help me solve some problem I was working on. In fact, as a grad student, most of the things I needed to learn weren't being taught in any of the classes available to me.

The choice isn't between being an autodidact or getting a Ph.D.; I don't think you can really earn the latter unless you have the skills of the former.