This is just how I wish I could modify the traits in Civ 4 to make them more interesting and worth playing. The changes I suggest are ones that go on top of the current function of each one:
Aggressive: +50% faster production of Stable, free Combat 1 for mounted and armored units.
Creative: +1
per 20% culture rate
Expansive: 50% faster production of Aqueduct
Financial: 50% faster production of Market, Grocer, Bank
Industrious: 50% faster production of Factory, Industrial Park
Organised: 50% faster production of Recycling Plant, remove factory bonus.
Philosophical: No change
Spiritual: +50% production of Monasteries
Imperialistic: Start the game with an extra settler
Protective: +25% defense in all cities (doesnt obsolete), all units take 20% less collateral damage.
Charismatic: No change
Aggressive: +50% faster production of Stable, free Combat 1 for mounted and armored units.
Creative: +1
per 20% culture rateExpansive: 50% faster production of Aqueduct
Financial: 50% faster production of Market, Grocer, Bank
Industrious: 50% faster production of Factory, Industrial Park
Organised: 50% faster production of Recycling Plant, remove factory bonus.
Philosophical: No change
Spiritual: +50% production of Monasteries
Imperialistic: Start the game with an extra settler
Protective: +25% defense in all cities (doesnt obsolete), all units take 20% less collateral damage.
Charismatic: No change
for its cottages, the AI will adapt to it. It takes trait yields into account, AFAIK. 


. Those things are plenty strong already. Also quite a boost to chariots..
. If that turned out to be overpowered, it could replace the production bonus. For aggressive, I don't know, maybe we could have units heal faster in enemy territory? That would offer little advantage for short wars, but it would be pretty nice for large-scale invasions.