When you break something destroyable in NS it just kinda breaks apart and vanishes and leaves a perfect hole exactly the size of the object it was covering (I.E. Vent Cover) where it is. Now this is a very workable tactic, but it's also kinda boring. With all the talk of weldable and breaking down doors and the like, why not make it look good? How about when you break through a vent or door, it creates a hole the size of your hit box (maybe a little bigger so you don't have a hard time getting through) and leaves the destructible still partly in place with some twisted and jagged metal. This also would mean if a skulk chew a hole through a door, it would have a smallish hole through it allowing other skulks to pass through (unless it gets welded) but if an Onos smashed the door, there would be little more then a couple pieces of scrap metal on the frame of the door. Nothing too big and fancy, just being able to literally tear a hole through rather then the generic "I hit it until it disappears". Perhaps have 3 or 4 types of destructible damage types, so if you bite/gore/slash through it makes the bent/jagged metal, but if you bile/acid it will instead make a more melted look to it. You could continue to damage the object after you make your hole to try and deceive the marines into thinking you have a bigger lifeform though this would take up more of your time. I think this would be a cool looking mechanism to implement and could to some degree help with strategy. "The door we just welded shut a minute ago is completely gone....this is bad"

Difficult to program and too complex. Keep it simple.

If everyone was as naive as you, we'd be playing Wolfenstein3D instead of Unreal3.
Open your mind.

It's a very good thought, and easily overlooked.
Unfortunately I don't know if it's possible on the Source engine to have area-specific breaks/damage on an object.
When I first saw the tech demos for HL2 and all the cool types of damage and materials I was excited, but when I play the game, it doesn't matter how or where you hit the palettes, they still break the same way.

Perhaps if they created 'new' materials which bent and buckled, but weren't subject to such specific damage as originally proposed, but looked semi-realistic in terms of the way they were damaged... having for example 4-6 states... starting with a little gap in the middle, then it peeling/bending back to make larger hole and more buckled looking until enough 'hit points' were achieved for it to totally bend back or break off the hinges?

hardpoints thats the answer in some games you have hardpoint on things where you can do specific stuff like in homeworld 2 you build stuff on them where maybe if you attack a specific harpoint on this door it will break though to make the effect of bending and buckling would not be as difficult as you imagine it to be so you could do it but not to a very large extent