
I’ve long intended to redesign the Craft and Knowledge skills from the ground up. I’ve even taken a shot at it a few times in the past. I’ve got a completed, but unpublished post from mid Summer where I went on a rather vitriolic rant about the failings of the skills system, based on one of those unsuccessful attempts. Regardless of the system’s failings, though, I do think that both of these skills are beneficial to the game and could be improved from their RAW state without fundamentally changing the way the skills system works. So with some new ideas in hand, I’d like to give it another try. This time moving more slowly, and “showing my work.”
It seems logical to me that any skill must be created with at least two different types of characters in mind. The Moderately Invested Character, and the Focused Character.
The focused character is one who has made this skill their top priority. Whether the skill is a crafting or knowledge skill, or any other skill for that matter, this character is determined to be the best at what they do. Through luck or point-buy, they start the game with an 18 in the associated ability score, and they select a race which grants them a +2 bonus to that ability score. Every four levels, they improve that ability score by 1 point, culminating in a +6 modifier at level 8, and a +7 modifier at level 16. The focused character also takes Skill Focus at first level. And, obviously, this character has selected a class for which this skill is a class skill, and places new points into the skill at each level.
Now, it wouldn’t be hard to take this further. Their are races with better than a +2 ability score bonus. There are magical items and spells which–temporarily or permanently–increase a character’s ability scores. Some races receive bonuses for specific skills, such as the gnomish +2 racial bonus to craft. Often, masterwork tools give characters a functionally permanent circumstance bonus to their checks. There are even magical items which increase competency with a skill, though in my opinion these should be almost entirely ruled out of the game for reasons which will become obvious in a moment.
If a person really wanted to max out their skill, and the GM was willing to humor them, then I think the skills system is so fundamentally, mathematically flawed that it would be impossible to create a well balanced skill. But when attempting to craft these skills, I will assume that the players are not quite so obsessive, and the GM is not so foolish to indulge them if they are.
The other type of character which the system must be balanced for, the Moderately Invested Character, is much simpler. They do not make this skill a priority, but it is a class skill, and they do put skill points into it at each level. Their associated ability score is a +2, which is above average, but not great. That, I think, is a sufficient level of involvement that a player should expect to see solid, level appropriate returns on their decision to invest in this skill, whatever it may be.
For all of these characters; the focused, the moderately invested, and every character who falls between; the skill ought to work ‘right.’ Certainly, within this gradation, there will be players who are more or less skilled than others. That’s fine, and in fact it is one of the benefits of the Pathfinder skills system. However, a moderately invested character should never feel as though the skill isn’t useful to them, nor should a focused character receive such significant rewards that they become overpowered. Players with less skill than a moderately invested character can be legitimately viewed as handicapped in the skill, and should not expect full at-level rewards from it. And characters with greater skill than a focused character can be considered overpowered already.
So how do the numbers work out?

Not great.
At first level, there’s already a variance of 6 between the moderately invested and the focused characters. By level 20 that variance has widened to 11. Those may not sound like very large numbers, but notice that a 10th level focused character has reached the same level of expertise that a 20th level moderately invested character can.
Forging ahead, now that we know which ranges the two character types will have available to them at each level, the question becomes: what acts should a character be able to perform at a given level? For example, according to the Pathfinder Core Rulebook, +1 swords cost 2,000 gold pieces. They’re also available for sale in large cities, so in the assumed Pathfinder campaign setting, +1 swords should be available to a character who has sufficient gold. According to the wealth by level guidelines, a level 4 character should have 6,000 gold, so I think it’s safe to say that a character is meant to have +1 weapons by level 4. If characters are to be able to craft magic items using the crafting system (as is my goal), then what should be the DC of crafting a +1 sword? 25? That gives the moderately invested character a 25% chance of success at level 4, and the focused character a 40% chance of success at level 1.
Clearly an additional layer of complexity is required here. Materials cost will obviously help limit this crafting, but it’s important to me that I avoid requiring feats in this system.
Further work on my part is required, but at this juncture I’m eager to hear what others think. Perhaps one of my betters can save me some time?