I think your formula is nice but maybe could value could be subtracted at the end for loss of time through getting educated (loss of youth). I presume it took a lot of graft to become an eye surgeon, maybe more so than a merger lawyer (during the uni/qualifying phase).
That's an interesting one. I know that my dad really enjoyed the process of becoming a doctor but not the process of studying for medical exams. He loves surgery, thinking fast and helping people out. In his field of expertise it turns out that watch-makers' hands are far more useful than an extensive knowledge of the retina.
By way of contrast, my uncle loved studying English. Those were years well-spent in his mind.
