Whenever a dwarf changes their value or belief, the game should be able to announce this, telling you the dwarf name, their resultant belief, the reason for change and previously-held belief or value.
i.e. "Zuglar Satiden, previously indifferent, has come to greatly value sacrifice from realization brought over mulling over being caught in the rain two years ago."
This would be controlled in announcements.txt with PERSONALITY_CHANGE token, with default settings being a single-line announcement at the bottom of screen in fort mode and no display in adventure mode.
I think this is could be a good idea for several reasons:
A) It's an important event in dwarf's life, with an impact that can be just as important to them as marriage or realization of a dream.
B) It's important to fortress overseer in that it may change substantially dwarf's suitability for fortress tasks and for living in the fortress as whole.
C) Given the two-year mulling period, these announcements would be relatively rare; it's even possible that this could be the only logging of given dwarf's name in gamelog at all for a given fortress.
D) Without drawing player attention, these can take a long time to discover, as most players tend to focus more on the skilled, troublemaking and visible dwarves and don't have a schedule for rereading the thoughts of dwarves.
E) Since there's already a thought for it, it should hopefully be quick to implement with no significant running cost.
Exact wording might be improvable, granted.
(Couldn't find this suggestion already posted with a brief search.)