I wonder if this is a viable solution:
By going up the Hero recruiting techs, not only do you increase the level of heroes spawning and such, but you increase the chance of your heroes learning a new Skill/Talent based on what they are doing. This can be tied in to the talents they already have.
For example, a hero with the research bonus can "learn" a talent depending if they:
1. sit in a city
- Research based city (research > +25?): learn +10%? research talent
- Arcane based city (arcane > +25?): learn +10%? arcane talent
- Gold based city (gold > 50+/turn?): learn +10%? gold talent
- defended a city: learn "City Defender" talent (+5 strength? when in city?)
2. not in a city
- not in a city/not doing quests for the last 50? turns: learn "Explorer" talent (+1 movement?)
- not in a city/stepped in a quest building for the last 50? turns: learn "Quester" talent (+ strength?/+ movement?)
- fought 10 monsters in the last 100 turns... + strength... etc
But they only have a % change to learn the talent, such as 0% when no Hero recruiting tech researched, 3% at first level, 5% at next level... etc which can also increase depending on the Adventuring level.
Now that I think about it, it doesn't do much to individualize heroes... but I'll post it just in case it helps someone with an idea.