I wish that bolts modified other things besides just damage and ammo count. If you think about it, well designed bolts should be more aerodynamic and influence missile speed and accuracy as well. This way there could be multiple bolts that fulfill a specific purpose. Would you like to be more accurate, but sacrifice some missile speed and damage? Or would you prefer to be more damaging but sacrifice accuracy and missile speed? It gives the ability to diversify bolts rather then the standard, pay more money to get more damage philosophy.
I don't know if this is possible with the current warband script though.