Anyone can ruin it deliberately, true - it works best with a cooperative group, not a competitive one. Modifying it for a competitive group would definitely remove it from the real of "useful introductory ideas", but would probably still be a useful exercise for more advanced classes.

Candy is also concrete and engaging - most people don't respond as enthusiastically to raffle tickets or $0.25. As part of a larger set of challenges, using play money with some sort of modest exchange of play money -> small prizes at the end of the session might work.