As a kid, I know that I would have be up against the edge dumping my popcorn on the street many stories down.
Ultimately that's probably the biggest impediment to this idea. Popcorn is no big deal, but the kid who drops a penny is going to kill somebody. Penny falling from that distance is like a bullet.
You'd need super finely-knit netting (no holes big enough for a coin) extending out in all directions far enough so that nobody could throw anything over them... and that netting would have be to strong enough to weather rain, snow, sleet, and the buildup of bird droppings.
It would probably ugly up all the views so much that it wouldn't be worth it, even if you solved everything else.