If sound was the only factor, the amp is probably more "important", but most people develop a personal relationship with their bass since it's the thing that you're actually holding all of the time and because it's so visible when you're performing, it almost becomes a part of your identity. For instance, when you think of bass players, you may forget their names, but you hardly forget which bass they play. I think that's why most spend more on their bass than they do on their amps, and in my opinion, rightfully so. I know both are mere tools, but amps seldomly inspire you to practice more and get better, you know?