Can I increase the sensitivity of the Sparkfun electret breakout board?

Using Arduino Audio
3

I'm little bit lost in your math:

averageReading = sumOfSquares/numberOfSamples;

runningAverage=sqrt(((averagedOver-1)*runningAverage)+averageReading);

You are calculating RMS and running average the same time?
What if I change it to:

averageReading = sqrt (sumOfSquares / numberOfSamples);

runningAverage = ((( averagedOver - 1 ) * runningAverage ) + averageReading ) / averagedOver;