Thanks. Yes there have been efforts to develop Duvvada as a satellite station, a few long distance trains make use of it by skipping VSKP, though at the cost of a technical halt at Simhachalam North.
My personal experience staying in Vizag for 2 years is that Duvvada is slightly too far away from the city proper, at least as of now.. so the best way currently to receive max patronage from Vizag is by using VSKP station. The city is expanding rapidly so Duvvada should gradually come into the picture more and more, imo.