A higher level (and thereby longer hoard) gives better chances of higher grades and rarity of items brought back. The amount of items brought back is dependent on Slvl. To put it in perspective, my level 100 pets with 100 Slvl tend to bring back stacks of 5 - 10 of whatever they find (not including capsules and eggs, which don't stack), and an average grade of 80. Hope that answers your question!