Unfortunately, these had such a large print run that it really isn't worth more than cover price (a couple of bucks at best). Opening the bag would not affect the price.
If however you have the Platinum edition (looks platinum), it may be worth a bit more ($20-$30).
It can be found in the guide under Adventures of Superman. Then look for issue #500.
I hope this helps.
"In my time nightmares walked among us... walked and danced. Skewering victims in plain sight. Laying their fears and worst desires out for everyone to see, just to make us laugh. And now nightmares are trapped inside the heads of humans. Pitiful echoes of themselves. I wonder whom they angered so to merit such a fate."