Currently around 71% of eligible voters are actually registered, and of those, only slightly more than half turn out to the polls. Voter turnout hasn't exceeded 60% since 1968, and it was 57.5% in 2012, down from 2008. Designating election day a national holiday would increase voter turnout and involvement in the electoral process, by making it easier for those with full time jobs and/or families to make the trip to their voting station.
Several other countries have done this already, including Austria(which typically has between 80-90% voter turnout), Belgium(consistently over 90%), and New Zealand(typically in the 70s and 80s).
If we were to create a holiday for voting, or even move election to weekends, we could easily see the number of involved citizens skyrocket.