(You can just cut your second post and edit it into your first one)

From a crafting/gathering perspective, I can see this working since there's no real way to get those Vs yet for them that I know of, but the battle materia grade Vs you can already get from PotD so I wouldn't be surprised seeing those go down as well.

Maybe what I would add is, that we have your idea to trade 10 in for the same type in but higher grade OR the option to trade 20 and get one of your choice but the same grade. I think that might help with the resistance materias and such selling faster as well. The reason I put it higher is because people might just find it cheaper to get the high teir resistance and just convert them to something they want.