I think having them last for more than one hoard would be the ideal; that way there is still a chance of finding nothing/not breaking even, but the chance of making a profit is higher/actually a potential outcome. ^-^;;

With the Potion/Evobar Ingredient Potion I used, the hoard (with a level 53 Common pixpet) returned with 2x Very Dull Magnesium. While this is better than not returning with anything (though I haven't had one of my 30+ level pixpet return empty-handed yet, knock on wood) it doesn't come close to offsetting the cost involved in creating the potion in the first place.

I've since used a Plant Pot potion (Grade 62: Pure) with the same Pixpet, who returned with fertilizer but no pot. I understand the need to prevent the market flooding so I don't want to pressure for too much change, and prices/availability will obviously change as the userbase grows and there are more people putting items into the market, but it just seems that considering how long plants take to mature and then grow produce, as well as finding the other ingredients you need at a high enough grade, having the potions last longer than one use would be nice.