When I was leveling crafting classes, I actually had a surplus of Clusters, a fair amount of Crystals, and I was practically starving for Shards.

There really should be some kind of conversion for this. Heck, I'd be okay with it going both ways, as everyone needs shards, everyone needs crystals, and everyone needs clusters, but at different intervals, so a player could convert a surplus of one to fill the deficit of another. Same elemental aspect of course. No one is saying anything about "Rainbow Crystals" or something foolish like that, just being able to either break down or trade in clusters for crystals and crystals for shards, then maybe vice-versa as well.