Why not rework the "skill check" system a little?
IIRC, skill checks involve the computer rolling 5 sets of "dice", a 1d5, 1d10, 1d15, 1d20, and 1d25. (That is, random number between 1 and 5, 10, 15, 20, and 25 respectively with even distribution.) Then comparing each roll to the skill level of the dwarf in question - if the dwarf has 3 ranks in the skill, and rolls a 4, 7, 2, 12, and 20 for each of the five "die rolls", then the dwarf's skill only beat one of the rolls, so the product gets only one rank up in quality, moving to "Well-crafted". If a dwarf has maximum possible skill (20), then only the fifth roll can possibly be lower than the skill rank of the dwarf.
Instead of this, we could use a more complex system, where we could potentially have more than five rolls, and skill checks for different actions skew the check in or out of the dwarf's favor when they are performing them.
For example, a standard skill check could be functionally similar to before by having 7 skill rolls, following 1d5, 1d10, 1d15, 1d20, 1d25, 1d30, and 1d35, and then adding 10 to a dwarf's skill level for the purpose of that one roll, ensuring he couldn't fail the first two, but having a chance at the next five. (Actually, not exactly the same, but I guess I can work on this a bit more later...) Instead of assuming you always succeed at the skill roll, you fail if you do not make any checks (but a skilled dwarf would always beat the minimum roll on almost anything), make an "inferior" product if you only pass one, make a normal product if you pass two, a well-crafted product if you pass three, and so on until you hit masterwork.
You could then make the "hard" stuff have less of a bonus to the skill level of the dwarf, or an outright penalty if something is very hard.
Inferior products may or may not work properly. An inferior door might not be made pet-impassible, for example, although you could still jam it locked or leave it open.
Inferior rolls in herbalism or the like end up with nothing, while a failed roll at herbalism might wind up with a poisonous plant misidentified and sampled, causing a symptom on the herbalist-wannabe.
Against this, we might have some sort of "apprenticeship" or "book" system for the peasants, but have it limited in how much it can train up to a certain skill level before they must graduate to doing, instead. (Of course, this idea has been brought up a hundred times in books threads all over the place.)