When I saw the topic title I instantly thought of weapon damage, or attack damage in general. Currently the game has force multipliers for the attacks of super-strong individuals such as vampires, but what'd be really neat is something like the following (pseudoraw):
[BLAH BLAH VAMPIRE PUNCH ATTACK BLAH]
[force multiplier:200%] <-- This exists already; I'm just putting it in for formatting comparison.
[randomness multiplier:50%] <-- What this would do is make the attack more consistent. Either the difference between the average and the random number 'rolled' could be halved, or the number of standard deviations between the average number and the random number halved. Or something else, if that would work better.
As for creature randomness, I'd like to see better reporting of a particular individual's abilities. I don't know about fortress mode, but in adventure mode a creature could reveal more and more about itself the closer it is to an inhabited area or the more often it attacks. For example, a quest-giver talking about a local and frequent menace could give information about its strength, speed, and material strengths or weaknesses (plus the size of its family...), but a quest-giver talking about something that has a distant lair and has only been spotted taking wandering livestock would only give as much information as quest-givers do now.