To start off. i havent played that many games, but for the ones i did i found that crafting usually has 3 categories:
-gear making (ie: blacksmithing) focused on creating armor and weapons, and generally items that have passive/ulimited uses.
-gear improvement (ie: enchanting) improving the properties of an item, adding stats or some effect
-consumable making (ie: alchemy) creating single use items with several purposes
Now, could you think of different crafting types (for this matter extracting profession which are only to obtain materials do not count)
Also all games ive seen the skill in this crafts is improved only by crafting. With few exceptions, like in Skyrim you can readbooks that increase a bit your skill in some of the crafts.
This leads to the materials being the only limiting factor for craft skill improvement, if you have the materials. you can raise the skill in little time.
The exception to this one is Eve Online (i dont know if there are others) in which you learn the skills from items or something, and it takes a lot of time (even months) to get those skill levels, but it does it on its own, you dont even have to play to gain the skill.
Also ive seen a lot of item obsoletization. I mean, the first items you make are very weak, and useless for higher levels. How about a system in whcih no item is absolutely better than other, but its usefulness depends on the situation, like the units on a well balanced RTS. So yo would start out with some few recipes and as your skill grows you get acces to greater variety and specialized items.
Any feedback appreciated. Thanks.