Unless the fares are prohibitive, I wouldn't suggest using miles on a flight like this. However, if you want to, Delta every now and then has fare sales to Mexico. Flights from the US go through Houston, Dallas seasonally, and Miami.

What are you specifically looking to photograph?

Mérida is one of the hottest cities in the country, and known to be one its safest, too. The historical center is small and predictable -- think public square near the main cathedral -- but pleasant nonetheless. The city's most famous tourist attraction is Paseo Montejo, a boulevard with a handful of 100+ year old mansions built due to the importance of henequen (an agave plant chiefly used to make twine and rope). You can also visit some haciendas within an hour's drive from Mérida.

For food, cochinita pibil (sour orange-braised pork with habaneros and red onions), sopa de lima (lima being a local plant), and chocolate (I like a place called Ki'Xocolatl, but of course it's subjective), among other Yucatecan delicacies.