...but how about give us the ability to create HIGHER quality crystals, too?

Of course that would make getting those too easy, so let's change something that differences it from downgrading:
Downgrading 3 crystals results into 5 crystals of a lower star level. How about when we want to upgrade 50 crystals into 30 crystals of a higher star level, we also use up 1-2 Alchemy Orbs of that star level?

You would be asking "why would we use alchemy orbs for that?" Because some of us have too much of those in the arsenal without actually having stuff to level up or heat.

TL;DR: Make higher star rated crystals with the use of a lot of crystals and alchemy orbs.