A common complaint on the forums is that bases tend to get completely destroyed when they're raided. I reckon this is because you need to disable all the braziers before you loot, so since they're all disabled anyway you may as well go and destroy everything. An idea that was brought up a time or two is dividing destruction of a base and plain old theft into two distinct systems. But I think that we can get the same effect by expanding the existing artifice system with two new sets.
The first set would be stealth artifices. They would serve to reduce damage from braziers, both bbile drain and permanent humour damage. The idea is that you could carry out a liftable object under brazier fire, or assassinate someone in the middle of a vault without destroying the braziers and come back out alive and well. This would, in essence, be the aforementioned theft system. Since this set isn't really intended for bashing your way in, it would probably need a lockpicking system to really shine.
The second set would be vandalism artifices. They would serve to increase damage against buildings. The obvious issue here is that high humour characters could simply use the stealth set since they don't really need a damage bonus, so we'd need a reworking of the way buildings are damaged in Salem. Tree walls come to mind here - the reason for their popularity is that they take a constant time to break through regardless of the assailant's phlegm. The same could be applied to all the buildings, ie give them a fixed destruction percentage per tick and make phlegm drain a constant (higher drain for higher soak objects). The only way to increase the % per tick and decrease the phlegm drain would be with the vandalism artifices. I think it should be possible to balance it so stealth artifices are always inferior for razing, and vandalism artifices inferior for stealing. Fields should have a really long destruction time, since they're so important and effort-intensive. Anyway, another advantage of this destruction system is that even newbies would be able to fix their construction mistakes, even if it would take a really long time due to lack of appropriate artifices.
Of course, focusing on one of these two sets would prevent getting high values for the other siege set, and more importantly for the combat set. Solo raiders would need to mix and match to strike the balance that fits them, and raiding party members could specialize in different roles.