Did you try using the app "Volume+ (Sound Boost)"?
Also, as other members have mentioned, I think you should have tried using other GNs, or replace your GN with a new one, before you completely return it. I personally never had an issue with voice quality. It could have been just your GN.
I couldn't feel it vibrate, I couldn't hear it ring. I was missing a much higher percentage of calls than I was taking. In fact, almost all incoming calls were missed unless I was sitting at my desk. I meet people and eat lunch out every day. I put the phone on vibrate as not to disturb others. I see who's calling and if important, I excuse myself. Most of the time I have to take the call no matter what. Main reason for return = consistently missing incoming calls. They are not going to change the vibrating mechanism on this device with a software update. The weak imperceptible vibrate is a manufacturer design flaw in my opinion. (I did download a couple of vibrate adjustment apps prior to returning the device.)
I have been perusing the internet and I see others are also posting about poor voice quality with their Galaxy Nexus, so it looks like I am not the only one. However, a few are blaming Verizon's network for the poor voice quality. I don't know who to blame, only that voice quality was horrible when I used this phone. If it was the network, exchanging the device was not going to fix the issue.