Turn it up. Too little volume for the application will teach you bad habits when it comes to dynamic control. If you can find a balance between the volume knob on the amp, the volume knob on the bass and your playing, you will be in a better position to be expressive. It's a whole other dimension for your playing. Great Guitar players understand this principal. You will see them adjust their guitar volume on the fly, and vary their dynamics to emphasize certain notes or passages. The danger of turning up the amp is having the power and not using it responsibly. It's more than enough to deafen you. Also, if you turn up and then everyone else does too, you are doing something wrong.
A good rule of thumb is to try to match the drums closely, then boost the amp about 10% and roll down the bass' volume and your playing down to give yourself breathing room. This way, you can have both softer passages, and the occasional authoritative moment.
tl;dr Turn it up, but play softer and ease off on the bass' volume a touch, this creates dynamic possibilities.