You are missing my point though, finding the best path is not actually required. Not only that but the game itself has mechanics by which paths are made and points that might need to be pathed to are created. Paths could be pregenerated as the map is dug out and items built within it, individuals could pick from pre-defined paths and then follow them.
A few examples of where this is actually better....
Currently lets say a dwarf plans to go down hallways A B and C to D. But he could go A B E D instead. Now as he enters B, a door in C is locked, dissallowing him to move C to D.
Under a "I path find every step" scenario, He immediately starts moving towards E and then D. This is highly unrealistic unless they all have walkie-talkies, but then, it "works" for invaders too.
Now under a less rigid scenario, maybe he chooses A B C D. Then gets all the way to C and sees the path is blocked, so he turns around and repaths. It is less efficient but more realistic, and potentially requires less expensive pathing.