There are quite a few spells that provide bonuses to all sorts of specific rolls, so I think thats easily doable on a case by case basis. I'm not sure, Nobles Parma, but I don't think there is any hard and fast magnitude/bonus ratio or any thing. Though some of the stuff in covenants might be a good guideline. As always I heartily recommend Items of Virtue from mystery cults for this sort of thing as they are pretty much defined as magical tools that help you do your job better.
A lot of it just depends on the creativity of your troupe and how generous they want to be. I had a blacksmith in one saga who had a magic item that warded him verses heat and flames. He was given a pretty good bonus because it let him touch his work directly. It also helped that he was giant blooded with a maxed out strength so he didn't always even need a hammer.