I would agree to a slight increase in Valkyrie spawn.
Like make three Valkyrie spawn within one hour (with different spawn times) and an additional spawn every 1.5 hours. That's a increase in the number of whisps, but it's not a amount that will make the price crash below 5~10 Token ea.
That should help regulate the price, while keeping the number of Randgris cards( that are supposed to be rare) low. Making more Rangrid spawn would probably make the price go even higher, because the MVPers will horde them and monopolize the item.
If more Valkyries spawn however, all players get the chance to hunt for the item.