The way i see it, if you achieve that 90 you should get a nice bonus and if you achieve 100 you should get a pretty big bonus at least twice as big as on 90. the way i see now is at 90 many crafting skills have this LOWWWWWWWW chance of making something that doesnt really make much difference either way and many 100 skills have bonus which doesnt make almost any difference, for instance lets take piety, on 90 you get a skill to give someone 3 luck, thats a great bonus, now on 100 you get a skill which increases that bonus by 0.5 so instead of 3 luck you get 3.5 luck, so you have to work VERY hard to get 100 skill points and all you get it is like less than 20% bonus. i would make it like 2-2.5 on 90 and 5 on 100. that would be a good difference and you would really try to get to 100.

same goes for other skills, like forging, you get 0.01% chance to make +20 quality weapon when quality doesnt matter and chance is 1 out of 10 000. and you get 0.011 on 100 which adds 1 out of 100 000 chance to make +20 quality when quality doesnt matter. so basically there is absolutely no reason to even try to get to 100 skill, only reason you should get to 90 is that you can make some weapons that you cannot before, but the actual unique bonus of making unique weapons is useless, it should be at least 1% to make unique item on 90 and like 2% on 100.

same goes for every skill that has that kind of bonus on 100 compared to 90, it should be around twice as much bonus at least, you have to REALLY want to take the skill to 100, it should be worth it.