We all know that Valestone and Moonstone have had no use since the removal of creating arcade gates. They have remained as a prestige like item. Bragging rights as to how many you had. Anyways, after reading the description of each item. I have got some ideas of what they can be used for.

Valestone
A fabled mineral of a vibrant, green color said to contain to essence of all natural life.

So Valestone is a mineral related to life. As such, I think this material could be used to create new healing items in the game, First-Aid Kits.

First-Aid Kit will be new consumable items that you can use from your inventory whenever you want. They will give you a variety of healing items. Vitakits, remedies, and health capsules. They'll also temporarily increase your max health. They'll have better effects at higher star levels. They start at 3*.

First-Aid Kit 3*

Improved First-Aid Kit 4*

Emergency Aid Kit 5*

First-Aid Kits will make for a great healing item to craft when going on a tough expedition(perhaps a shadow lair?). They are not overpowered in the slightest as they require lots of materials to craft.

Moonstone
A fabled mineral of a brilliant blue color said to contain the knowledge and origins of all worlds.

New Trinkets

Navigator

This will allow players who like to grind levels a much easier way to check if a level has a specific scenario they are looking for, and will greatly speed up grinding times. The crafting recipe isn't insane nor is it too hard to get. Since the begining of the game you should be collecting Valestone, and will not have much to grind when you want obtain this item.

Overloader

This will be a endgame trinket that players will want to grind for. Completely, changing what weapons you will want to bring in each level. Bringing Voltedge to a level with Shock Enemies will be very useful when you really need that crowd control.