One other thing about non-repeatable alchemical formulas occurs to me: it can be used to create MacGuffin situations. If the PCs and the BBEG both get the same alchemical formula from the same source (maybe some mad inventor whom the PCs rescue from BBEG's dungeons), and they both want to use the Potion of Meteoric Destruction, then it becomes a race against time to see who can gather the necessary ingredients first--whoever comes in second winds up with an inert potion. This is true even if the PCs decide to destroy the potion after making it, instead of using it.
I also like the idea of generalizing this "invent-your-own/usable-only-once" thing slightly to both rituals (not in the 5E jargon sense, more in the Dominions 4 sense) and potions, with the difference between them being that a potion is a delayed ritual in liquid form whereas a ritual takes effect immediately. Perhaps lichdom is a ritual, which means (1) each lich takes a unique path to lichdom; (2) you never know for sure if it's going to work until you complete the ritual and roll the final Arcana check. If the final step of the ritual involves something like cutting out your own heart, that final skill check might be pretty nerve-wracking.
At this point I'm starting to think seriously about actually formalizing the ideas from this thread and using them in my actual game.
