The description on the reverse side of the New Frontier postcard is interesting --
It references an "Out of this World" theme, with the "Venus Room" (showroom), "Cloud 9 Lounge" and the "Planet Room".

After the original Last Frontier's wild west theme, looks like the remodel to the New Frontier in 1957 took on an outer space theme. That's in parallel with the late-1957 launch of the USSR's Sputnik satellite and space race ... and just before the 1958 opening of the Stardust nearby.

It wasn't just Jay Sarno that created themed casinos (Caesars Palace and Circus Circus), though he was a master in his time!

The whole country was preoccupied with space in the mid-to-late 1950's. Even Disneyland had both a Frontierland and Tomorrowland when it opened in 1955.