Odd, we almost always get them open, but what I find is that they have junk loot in them... Like a cats eye agate or a one-time use potion (don't care what it does, pass).
If the chest is right by the exit, ok, but if it's deep in a 65 dungeon, make it something halfway decent, like a named drop or something. Or else, just take them out, you could have chosen another mission in the time it takes to backtrack and figure out chests.
Sinfonian