When did vision evolve for the first time?
"To me, it also makes sense that the evolution of sight would have accompanied the evolution of advanced brain functions in almost every case." 


Not necessarily! For instance, think of phototropism: the plant detects the presence of light and uses it to grow towards the light, but that's a very simple process regulated by auxins. Or the light-sensitivity (phototaxis) shown by Euglena, a single-celled protist, which reorients its entire body towards a light source. Really simple vision (is there a light, and if so, where is it?) can help organisms absorb more energy than rivals, giving them an evolutionary advantage.