Is there a second Mona Lisa?

National Post:

“Scientific tests don’t demonstrate the authenticity [and] the autography of a painting, but demonstrate it’s from a certain era, whether the techniques are similar or not,” Vezzosi told The Associated Press in French. “Here, there are many open questions,” before waving his hand over the painting, as a security guard with folded arms stood nearby.

Ever since the 16th century, several historical sources suggest that da Vinci painted two “Mona Lisa” versions. One was of Mona Lisa Gherardo around 1503 that was commissioned by her husband, Francesco del Giocondo, the foundation said. Another — the one in the Louvre — was completed in 1517 for Giuliano de Medici, da Vinci’s patron. That theory fits with da Vinci’s tendency at times to paint two versions of some of his works, like the Virgin of the Rocks, the group said.
Foundation members say it’s unrealistic to think that the woman sat twice for a portrait, but that the meticulous, mathematical approach suggested that Da Vinci may have projected in his mind what she would have looked like between the first alleged “Mona Lisa” and the “Mona Lisa” in the Louvre.
However, the foundation acknowledged that the “Isleworth Mona Lisa” remains unfinished, and that da Vinci didn’t paint all parts of the work. Still, the group pointed to newly discovered evidence in 2005 from Heidelberg, Germany, that suggested da Vinci was working on at least the head of such a painting in 1503.

I’ve seen the original, and while it was nice, I’ve never understood what makes it a masterpiece.
Okay that’s funny. I just read on NPR that it’s famous because it was stolen!  So it’s famous because it’s famous.

Before its theft, the “Mona Lisa” was not widely known outside the art world. Leonardo da Vinci painted it in 1507, but it wasn’t until the 1860s that critics began to hail it as a masterwork of Renaissance painting. And that judgment didn’t filter outside a thin slice of French intelligentsia.
“The ‘Mona Lisa’ wasn’t even the most famous painting in its gallery, let alone in the Louvre,” Zug says.
Dorothy and Tom Hoobler wrote about the painting’s heist in their book, The Crimes of Paris. It was 28 hours, they say, until anyone even noticed the four bare hooks….
All of a sudden, James Zug says, “the ‘Mona Lisa’ becomes this incredibly famous painting — literally overnight.”

Any art experts out there want to explain why the painting is worthy of fame, beyond the fact that it became famous from a heist?