Currently, the material that a bow (or crossbow) is made of only affects it's effectiveness as a bludgeon in combat. Perhaps we could also realistically simulate material properties for their ranged function as well?
What I'm suggesting is that a bow made of a material with higher tensile properties will have lower effectiveness for smaller creatures or those with lower strength. For example, Freengus the Kobold will have some serious trouble trying to pull the string on a bow made of iron in order for the arrow to go anywhere meaningful. Meanwhile, Urist McMuscles or Mr. Giant over there will have no trouble pulling on it, and will gain whatever benefit it may yield to them (probably higher missile velocity than using an ordinary wooden bow).
This can apply to crossbows as well - A crossbow with a steel bow (i.e. an arbalest) may boast a greater shooting force than a wooden one and be able to punch through the heaviest armor, but can boast a slower reload time (Once Toady has fixed the fire rate for them compared to bows) and may require a Windlass in order to cock and load it.
This will give more variation to Fortress mode as well as Adventure mode - It will give reason to actually use both wooden crossbows as well as metal ones, dependent on whether you want to compromise speed over power or vice versa.
Good or no? Post below!