Again - as all - it is about planning.
When you play impossible you start only with few crystals (20 or so) and I would not wonder if you would need more for the same spell upgrades (but for 80% I am sure that the price is the always same)
Planning is:
You have few runes of magic and mind - you could add them into alchemy, or chaos magic/ which one want choose?
At the beginning you have very few spells and even fewer are worth upgrading... so you won't save that much with alchemy, but will be more effective with upgraded chaos magick. BUT... But you may have level 3 chaos magic, spent all your crystals on fireball, you will find ice snake... hell! Darn! - where to get crystals now? You get hardly enough crystals to get ice sanke on second level, and you find fire rain... DARN! DARN!
In such csae you would love to use more runes in achemy sooner...
Is Alchemy usefull? TOTALLY !
Is it usefull when you brainlessly use all your runes in this skill at the most earlier game stage? I would say NOT.
I just say : thank you for this great skill... and add : I will use it for my benefit, wisely.