We all know it: Luminite, Crimsonite and Dark Matter are where it's at. Valestone and Moonstone only have a "real" use in Geological Survey missions.
This is unfortunate because, aside from being near useless, nine times out of ten people ignore them completely. If there's a batch of minerals, let's say one Crimsonite and the rest are Valestone/Moonstone, someone is gonna nab the Crimsonite and abandon the rest completely. It's a waste.

Ideally, I think they should have an easy, convenient use, while still making them less valuable than the big three minerals.

The idea of Mixed Motes is that combined, the two minerals could be used to subsitute for any of the other three. For example, a Shadow Mote needs 5 Dark Matter, or alternatively it could use 5 Valestone AND 5 Moonstone. It requires more minerals overall, but allows the two useless ones to fill in as a substitute, a proper back-up option if the one you're going for isn't available to be found.

(and obviously it would extend to the higher level pet foods as well)

I just had this idea, thought it was neat, and couldn't not share it. Quality-of-life updates is the name of the game.