I have an idea to restore 1.0 crystal conversion,
yet not breaking economy and give RMT/bot a profit:

1. Only available as breakdown from cluster
2. Requires additional materials for the breakdown, I suggest using elemental resist materia + grade 4 carbonized matter
3. Each crafting class except ALC & CUL is capable of breaking down 1 type of element only
4. Maybe a new material from unspoiled node which a ALC can craft something with it for the breakdown recipe

Reasons:
1. Upgrading crystal destroy a DoL's role to supply them
2. Materia and Unspoiled materials are less likely to be mass produced even with bots farming, it's used to keep the difference between human DoLs' and bot DoLs' production rate smaller
3. DoLs still keep their role to supply shards to crafters, the 1 element per class is again to make things more complex to let RMT has direct influence on the market. It also establish a trade network between crafters.
4. Make things more complex once again

Impacts:
RMT/bot to market - They need to seperate their bot teams for different items, they cant really mass produce as easily by using bot to a typical node. And there's the barrier of using materia.

DoL to market - Still providing their stuff to crafters, a bit less junk items from their gathering list.

Non crafters - Less junk materia, more intention to spiritbond stuff