So basically what I gather from all of that is you want a PhD because when you “retire” you want to teach, and you believe that degree is…what, necessary? Opens more doors?
Really that depends on what you want to teach. To be perfectly honest, if you plan on teaching the world you know (finance), a PhD is not necessary. Certainly not with your credentials. Business schools (at least the good ones) want real world experience. They want instructors who know (and can teach) the students the things they need to know to get hired by the big firms. 2.8 masters degrees and a couple of decades in the trenches is plenty.
Really, is it more just a personal thing? I get the sense that you just really want to be back in school…