Plenty of games have variable difficulty tasks, with different degrees of character skill to accommodate varying levels of ability. FUBAR has always had the idea of characters rolling three dice in things they aren't particularly competent at, four dice if they have some level of skill, and five dice if they are well practiced in the types of actions necessary to complete a task. In the core game, a success was a success, a failure was a failure. Not quite a simple binary, because the fail option is split into "fail, but you can try again", and "complete fail with no chance of a retry". There's the chance of suffering a sacrifice every time a task is attempted as well...so a chance of a retry also means a chance the more needs to be sacrificed to complete an action.
Positive and negative traits were always messy in the system, so I've clarified some things. I don't think this streamlining makes the game more "realistic", but it makes things more cinematic and helps to emulate the genre tropes of building adrenaline and cumulative higher stakes.
At various iterations of the game, positive traits added to the chances of success, or reduced the difficulty of tasks. Conversely, negative traits reduced chances of success, or increased the difficulty of tasks. The game already has varying numbers of dice to reflect the chances of success based on character skill, so the idea of positive and negative traits similarly manipulating the same things was a bit confusing for many players and ended up getting scrapped in play because of this. Another version of the game saw positive traits and negative traits balance out, with any excess traits providing a secondary pool of dice (excess positive traits being rolled as potential extra "successes", and excess negative traits rolled as potential extra "sacrifices"). This slowed things down, with two distinct sets of rolls for every action...again, not optimal.
The latest thought is to simply apply the positive and negative traits as multipliers of outcome. A task doesn't get easier if you've got positive traits, nor does your skill level increase, instead a positive trait lets you get twice as much done with a standard success (two positives get triple the result done, etc.) Possessing negative traits adds to sacrifice in the same way. If you've got both that means the chance for big success at the risk of big sacrifice, but a character could also play it safe by cancelling out positives and negatives. This also means traits play a more significant role in resolution as they accumulate through the course of a story. The rolls don't stagnate because the chance of success and sacrifice remains the same, but the stakes rise.
Naturally if it works here, it will cascade across to Walkabout when I get back to work on that project.