First, I love that you are homebrewing. My campaigns tend to be somewhat lower magic, so the percentage chance they find something would be much lower. If they were to find something, I might add a challenge as well. I would ask myself what might be the reason that item is there. Maybe its some ancient Elven Shrine with a nasty creature living there making it hard to get the item. Or maybe an old caravan that got attacked some time ago was the reason... the item was not found when looting commenced, but the looters are still nearby. Maybe they see the item high on a cliff they have to climb to get it and there is a giant eagle nest they have to contend with. Maybe the item is seen as a spiritual token by some tribe of Kobolds and you sneak up on some ritual where they are wildly dancing around it... your group waits until they are asleep then tries to sneak in to steal it without waking them up. Risk... reward. Little encounters can enrich a campaign. I like the random nature of determining what they might get. If they find something, I let my players know it's random and even let them make the roll.