Make the spice blend: Combine the salt, chili powder, ancho powder, paprika, garlic, guajillo powder and lime zest in a small bowl; set aside.
Make the crema: Combine the mayonnaise, sour cream, cilantro and 1/2 teaspoon of the spice blend in a medium bowl; refrigerate until ready to use.
Cook the corn: Heat a grill to high. Brush the corn with vegetable oil. Grill, turning occasionally, until tender, 8 to 10 minutes. Let cool.
Cut the kernels off the cobs and transfer to a large bowl. Add 1/4 cup of the crema, 1/2 teaspoon of the spice blend and the cotija and cilantro; stir to combine. Top with more cotija and cilantro and sprinkle with more of the spice blend. Serve with lime wedges.