Materia level up-gradable?

[Raldo]

Hasrat is definitely correct. There are a handful of fringe cases where "trash" materia is useful, so you may want to check the markets before you just sell them to an NPC vendor (though the last time I checked, almost all of them were pretty worthless). I suppose it's also worth mentioning a few other niche uses of "trash" materia...

• Spiritbonding: Gear will spiritbond faster if there's materia melded into it. The spiritbond increase is the same regardless of type or tier of materia. For example, some people will socket trash materia onto their DoH gear while crafting stuff in bulk in order to turn it into materia faster. Side note: If you are doing this, don't forget to try to unsocket your materia before you convert the gear into materia! There's no reason to waste perfectly good trash materia.

• Desynthesis: Desynthesizing gear with materia socked gives you a small boost in your desynthesis success rate. I think it's a 5% boost per materia (regardless of materia type or tier).