The mystic crystals and metals used in wand making were never alive and thus never had any magic of their own. This is why we call these crystals and metals merely mystic rather than magical. While they cannot strengthen magic spells, these special crystals and metals are able to focus magic spells.
When these mystic crystals and mystic metals are used on a wand's handle, shaft, and tip, they help focus the magic spells, resulting in two benefits. The spells are more likely to strike their targets, and more of the spell's magic is likely to be transferred to these targets. Thus, although mystic crystals and metals do not directly increase the strength of magic spells, they can have a similar result.
In addition to focusing magic spells, mystic crystals and metals have a second important purpose. When used to make a wand's end cap, they act as a reflector, ensuring that the spells fly forward and do not accidentally backfire onto the mage that casts them.