An issue I ran into is when you have 3 of the same treasure, they stack up and you can't split them. To get certain steam achievements, you have to have 1 of each item, including treasures. Keeping a stack of them is obviously not optimal. Even without the achievements, it is nice to hold onto treasures sometimes and being able to sell them off one at a time would be an improvement.
Yes, when you equip them to a character only one item will be removed from the stack. Since treasures can't be equipped this doesn't work for them.