Comparing two imbalanced signal transmission
If you do the maths you will find that the impact depends on the ratio of the imbalance to the RX common mode impedance, 100R:100k for example will give a common mode to differential mode conversion of -60dB, 100R:10k will be -40dB, 100R:1k will be -20dB and so on, it is just a potential divider. 

It is for this reason that one figure of merit for a differential receiver is a very high common mode impedance, and why things like the THAT Corp bootstrapped line receivers are such a brilliant idea. 

There are plenty of microphones that are impedance balanced, and they work perfectly well.