Your thoughts inspired a thought in me:
Alchemy could work something like this:
You need materials, time, expertise, and a bit of luck.
When using alchemy to make anything, you roll 3d20, and add the averages of your bonus's in arcana, nature, and history. The hardest of the hard stuff would require something that could only be gotten by rolling an average of a 19+, and being proficient in nature, arcana, and history, at level 17+. If you didn't get your roll, then bad stuff happens, like you lose a limb and/or the materials all turn to goop.
For stuff that wasn't the hardest of the hard god-tier stuff, i.e., stuff that you'd usually want more than one of, you can have yields. For the easiest stuff, like weaker healing potions, you don't want low level characters being able to make these willy nilly, even if they get all of the materials. So, you have the yield be goop for rolls between 3-40; the yield could be 1 for 41-60; 2 for 60-65; and goop for anything over 65.
Using yields, you can be extra sure that alchemy won't ever be overpowered. You can gather all the materials, know the recipe, and spend all the time doing it, but if you're trying to craft something out of your league, i.e., where a yield of one requires something like 65. A first level character could obtain such a substance, but they'd have to roll perfect 20's, and be proficient in arcana, nature, and history. Plus, they'd have to spend all the time and gold on gathering the materials, and actually researching/discovering how to craft it.
Then, from the designer's perspective, all you have to do is make sure that the substances at least require hard to find materials, and then come up with a general distribution of what rolls got you what event for each substance. Then, from the Dungeon Master's perspective, if they think that the designer's roll distributions made things too easy, he could just multiply everything by 1.1, and round down, or multiply them by .9, and round down.
What do you guys think? Has anyone already done something like this?