These two definitely belong to the same family. They're similar values, but the hues are not quite a match. I'd say Playa del Platinum is a touch dirtier and dustier. It almost looks like Playa has a hint of green in it when next to Sand Tropez. Another difference is that I used three coats of Playa del Platinum but only two of Sand Tropez.
While looking for Playa del Platinum, I came across Body Language, so decided to try that out against Sand Tropez, too.
Again, related, but not dupes. Also again, a three coater compared to Sand Tropez's two. Body Language is noticeably lighter than Sand Tropez, and reads cooler in tone. There's no need for me to destash any of these on the basis on dupey-ness. On the basis of still needing to keep clothes in my closet instead of filling all the space with nail polish—that's another story.
(P.S. Did you vote for Locavore yet?)