If you grab the biggest mineral, you get more minerals. If you have more minerals, you can craft the pet food mat. If you don't like the pet food mat, you can trade it for someone else's pet food mat. And then you can ask someone on your friendlist for the trade! Yes?
But if you grab the smaller mineral, it's not equal value.
So the mathematical equation behind it is... I don't know. I'm too lazy to make it. But trading minerals is faster than doing a whole level again for the same small mineral, isn't it?
Trading minerals would definitely be interesting. It could fill in that gap of people wanting to sell the minerals just like the old days.
However if more sprites are being implemented, I feel like this would be the best time to do this. We can already trade food, so in the we're just trading dust to each other right now.