Stir together lime juice and agave nectar; add to a blender, along with pineapple juice, pineapple, triple sec, tequila, and ice. Blend until smooth and frothy.

In a small shallow bowl or saucer, combine chili powder, sugar, and salt. Rub lime wedge around the rims of four glasses, then dip the glasses in the spice mix to coat. Divide the drink among the glasses and serve with lime wedges.