Concerning Potent Potions, when I wrote that, I thought about sticking a caveat in there, because it is a debatable point, but I thought it would derail my overall explanation. I do think, and I think Sanctaphrax would agree(?), that it's an appropriately-powered supernatural stunt. (I call it a supernatural stunt because only a character with Ritual or Thaumaturgy could take it and have it DO anything.)
The specialization vs. focus item debate is somewhat simpler in the context of Thaumaturgy, because you don't have the offensive/defensive split of Evocation focus items. One refresh of Refinement gives two points of augmentation, either by spec or focus item, in the same manner. Specialization must follow the pyramid, though, and focus items could be lost or broken, temporarily removing their bonuses from the practitioner's use.
In a sense, Potent Potions is the best of both worlds. It need not follow the pyramid, and as a stunt, it's not particularly removable by plot circumstances. It also grants the same net bonus as Refinement for the same price. If that was it, the stunt would be overpowered, but it's limited by a restriction to Potions, and therefore would not apply its Power bonus to enchanted items. Sure, if the Crafter in question decided not to make any enchanted items, the stunt would always apply, but I'm not overly concerned with Potent Potions being a bit overpowered in a character that's only using half of Ritual: Crafting.
As a practical matter, I'm still of the opinion that sinking one Refinement into focus items to boost Crafting Strength is slightly better than Potent Potions because the points of Power boosting your enchanted items outweighs the risk of focus item destruction. I think this is especially true for a Crafter, because Crafting focus items tend to stay in your lab, rather than travel with you in the field.
Is there a consideration I've overlooked, Sanctaphrax? I'll admit, I'm short on actual experience playing the game, but the above was my reasoning process, such as it is.
