I will be the nice guy and let you into a little secret. You are going to have to put probably close to 1500lbs to make your car look "lowered". Not slammed, like Prokit lowered. I am guessing but I had 350lbs of rock in my trunk and it made no difference. Now, that is almost twice the weight capacity of our cars. That makes it extremely dangerous. I have ridden with 5 people in my car who were all on the heavier side (besides me), and my car actually had a very noticeable difference in handling and breaking, in a very negative way.
So, it's not just gas mileage and acceleration.