Fantasy buildings are so last century in Las Vegas. Now the buzz is about fantasy experiences, the latest of which are tied to an MGM Resorts casino loyalty program called M life Players Club. The payoff isn’t just in coupons for dinner or hotel room deals but also in the kinds of special-access events at MGM properties that merit bragging rights—a day of directing the songs at the Fountains of Bellagio, a cameo appearance in a Cirque du Soleil production at Aria Resort & Casino, or cooking lessons with....