We need more axes and hammers! Dwarves are famed for their ingenuity, but also for their stout warriors. Traps should still be powerful, but I think it should take more effort to set up truly devastating traps.
I think weapon traps should be manually reset unless they have a power source. This would make power sources even more useful. When a trap is sprung it has used up all it's stored energy, it shouldn't be able to reset itself without a force to reset it. Also, enemies should have a chance to dodge traps based on agility, and how well oiled the mechanism is. They could be oiled with animal fat or something. The odds of a trap jamming could be based on how well oiled it is and the quality of the mechanism.
Weapon traps need a lower limit on how many weapons you can cram in them, and the parts shouldn't last forever. Stone mechanisms should break on occasion, happening much less often with higher quality ones, and the weapons themselves could wear. Metal mechanisms, if they're implemented, would never break, though they could rust if you pick a bad metal, and I don't need to tell you how nasty rust is.
Actually, mechanism jamming, mechanism breaking, and bogged down mechanisms would be great in everything. Imagine having a siege when you're not prepared. Luckily, you just finished a drawbridge! However, as you pull the lever the mechanism jams and the drawbridge stays put. Fun!
As for crossbows, making them more quality dependant would be nice. Rate of fire, accuracy, force, and reliability should all be factors. Currently a group of well trained marksdwarves are an unstoppable force when working individually, when in reality they're support units. They shouldn't do a terribly huge amount of damage, since if they have enough meatshields and some fortifications they're pretty much untouchable, the advantages are clear enough.