Assuming we have an analog differential signal trace that we must route from the connector to lets say an ADC, 24 bit or 32 bit kind as i dont think lower resolution ones are not affected by this. What we would like to happen is to preserve the signal as much as possible so that our ADC can read as accurate as possible.

I have read that in order for traces to be least likely to be affected by external interferences it is best to surround the traces by ground planes above, below an beside. But in order to execute this on a pcb (lets not factor external shielding) only we must have a lot of vias

From what i know adding vias adds capacitance which we might not want especially at high frequencies? So At what frequency do you think 4-6 vias will start being a problem ? Is 50kHz still in the clear? How About 1MHz or 100Mhz?

At what point do you think that the added EMI protection is not worth due to signal being affected to much by the vias an the traces should be all be brought back up to the top layer?